The brain and behaviour (chapter 4) Flashcards
1
Q
What is the nervous system? What is it made up of?
A
The body’s control centre which is made up of two kinds of cell: neurones and glial cells
2
Q
What are neurons?
A
The functional building blocks of the nervous system. Cells which transmit the electrical activity which underlies psychological processes
3
Q
What do neurons send around the body?
A
A combination of electrical and chemical signals throughout the body. Some of these signals are simple and control automatic body functions like the heartbeat. Other signals are extremely complicated and involve a much larger network of neurons. It is the electrical and chemical signals of neurons which make up our mental activity.
4
Q
What are glial cells? (support and supply cells)
A
From the Greek for ‘glue’. Cells surrounding the neurons holding them in place, providing nutrients neurons need and isolating toxins that would harm the neuron
5
Q
What do neurones determine?
A
The ways in which we think and process information are determined by the ways in which neurons pass electricity through the nervous system. The power of our mental processes is determined to a great extent by the numbers of these neurons and the numbers of connections (synapses) which can be made between different neurons.
6
Q
What does the average male brain contain (neurones)?
A
The average adult male brain contains 86 billion (86,000,000,000) neurones, which is something like the number of trees in the Amazonian rainforest. If we take it that each neuron possesses about 600 synapses with other neurons, then that gives us 51,600,000,000,000 neurons. The brain clearly has a lot of processing power
7
Q
What are the 3 major types of neurons?
A
3 major types of neurons carry out the system’s input, output and integration functions.
1) sensory neurons
2) motor neurons
3) interneurons
8
Q
What are sensory neurons?
A
They carry input messages from the sense organs to the spinal cord and brain
9
Q
What are motor neurons?
A
They transmit output impulses from the brain and spinal cord to the body’s muscles and organs
10
Q
What are interneurons?
A
They perform connective or associative functions within the nervous system. They far outnumber sensory and motor neurons and it is the activity of the interneurons that makes possible the complexity of our higher mental functions, emotions and behavioural capabilities
11
Q
What are the 2 major divisions of the nervous system?
A
The peripheral and central nervous system
12
Q
What is the peripheral nervous system?
A
It contains all the neural structures that lie outside the brain and spinal cord.
Its specialized neurones are mostly sensory and motor neurons, and help carry out: (1) the sensory input functions that enable us to sense what is going on inside and outside our bodies; and (2) the motor output functions that enable us to respond with our muscles and glands.
13
Q
What are the 2 major divisions of the peripheral nervous system?
A
The somatic nervous system and the autonomic nervous system
14
Q
What is the somatic nervous system?
A
It consists of sensory neurons that are specialized to transmit messages from the eyes, ears and other sensory receptors, and motor neurons that send messages from the brain and spinal cord to the muscles that control our voluntary movements. Sensory neurons group together like may strands of a rope to form sensory nerve, and motor nerves. As you read this, sensory neurons in your eyes are sending impulses into a complex network of specialized visual tracts that course through your brain. (Inside the brain and spinal cord, nerves are called tracts.) At the same time, motor neurons are stimulating the eye movements that allow you to scan the lines of type and turn the pages. The somatic system thus allow you to sense and respond to your environment
15
Q
What is the autonomic nervous system?
A
The body’s internal environment is regulated largely through the activities of the autonomic nervous system, which senses the body’s internal functions and controls the glands and the smooth (involuntary) muscles that form the heart, the blood vessels, and the lining of the stomach and intestines.
16
Q
What is the autonomic nervous system largely concerned with?
A
Involuntary functions, such as respiration, circulation and digestion; it is also involved in many aspects of motivation, emotional behaviour and stress responses. It consists of two subdivisions: the sympathetic nervous system and the parasympathetic nervous system. Typically, these two divisions affect the same organ or gland in opposing ways
17
Q
What is the sympathetic nervous system? Example.
A
Has an activation or arousal function and it tends to act as a total unit. For example, when you encounter a stressful situation, your sympathetic nervous system helps you confront the stressor in several ways. It speeds up your heart rate so that it can pump more blood to your muscles, dilates your pupils so that more light can enter the eye and improve your vision, slows down your digestive system so that blood can be transferred to the muscles, increases your rate of respiration so that the body can get more oxygen and, in general, mobilizes your body. the sympathetic nervous system governs the so-called fight-or-flight response.
18
Q
What is the parasympathetic nervous system?
A
It is far more specific in its opposing actions, affecting one or a few organs at a time. In general, it slows down body processes and is involved in maintaining a calm state. Thus your sympathetic system speeds up your heart rate; your parasympathetic system slows it down. By working together to maintain equilibrium in our internal organs, the two divisions can maintain homeostasis, a delicately balanced or constant internal state.
In addition, sympathetic and parasympathetic activities sometimes coordinate to enable us to perform certain behaviours. For example, sexual function in the male involves penile erection (through parasympathetic dilation of blood vessels) followed by ejaculation (a primarily sympathetic function)
19
Q
Define homeostasis —
A
A delicately balanced or constant internal state
20
Q
Define the central nervous system (CNS) —
A
Contains the brain and the spinal cord, which connects most parts of the peripheral nervous system with the brain.. Although some of the peripheral nervous system enters the brain directly, most of this happens through the spinal cord
21
Q
What is the spinal cord?
A
Most nerves enter and leave the CNS by way of the spinal cord, a structure that in a human is 40.5 to 45.5 cm long and about 2.5cm in diameter. The vertebrae (bones of the spine) protect the spinal cord’s neurones. When the spinal cord is viewed in cross-section, its central portion resembles an H or a butterfly. The tissue in the centre of the spinal cord has a grey appearance, and is called the grey matter, The tissue on the outside of the spinal cord has a white appearance and is called white matter, We will discuss the significance of these different types of tissue in the next sections. Entering the back side of the spinal cord along its length are sensory nerves. Motor nerves exit the spinal cord’s front side
22
Q
What are spinal reflexes and how do they work?
A
Some simple stimulus-response sequences, known as spinal reflexes, can be triggered at the level of the spinal cord without any involvement off the brain. For example, if you touch something hot, sensory receptors in your skin trigger nerve impulses in sensory nerves that flash into your spinal cord and synapse inside with interneurons. The interneurons then excite motor neurons that send impulses to your hand, so that it pulls away. Other interneurons simultaneously carry the ‘Hot!’ message up the spinal cord to your brain. But it is a good things that you do not have to wait for the brain to tell you what to do in such emergencies. Getting messaged to and from the brain takes slightly longer, so the spinal cord reflex system significantly reduces reaction time and, in this case, potential tissue damage
23
Q
What is the brain and what does it do?
A
As befits this biological marvel, your brain is the most active energy consumer of all your body organs. It accounts for only about 2% of your total body weight, but it consumes about 25% of your body’s oxygen and 70% of its glucose, It never rests; its rate of energy metabolism is relatively constant day and night. In fact, when you dream, the brain’s metabolic rate actually increases. The brain, like the spinal cord, is composed of grey and white matter, but this time the grey matter is outside the brain, and the white matter is on the inside. The grey and white matter are composed of the different parts of the neurons which make u the brain and nervous system. The grey matter is made up of the cell bodies of neurons. The white matter is made up of the long connecting parts of neurons, the axons. The axons connect various levels of the brain and spinal cord with each other.
24
Q
What are neurons?
A
Specialized cells called neurons are the basic building blocks of the nervous system. The estimated 85 billion nerve cells in your brain and spinal cord are linked together in circuits, not unlike the electrical circuits in a computer. Neurons can vary greatly in size and shape. For instance, neurons found in the brain may be extremely short and only millimetres in length, but neurons situated in your spinal cord may have an axon that is long enough to extend to the tip of your fingers.
25
What are the main parts of a neuron?
Each neuron has 3 main parts: a cell body, dendrites and an axon
26
What do each part of a neuron make up in the nervous system?
The cell bodies and dendrites make up the grey matter of the nervous system, and the axons make up the white matter.
27
What is the soma?
The cell body, or soma, contains the biochemical structures needed to keep the neuron alive, and its nucleus carries the genetic information that determines how the cell develops and functions
28
What are dendrites?
Emerging from the cell body are branch-like fibres called dendrites(from the Greek word meaning 'tree'), specialized receiving units like antennae that collect messages from the neighbouring neurons and send them onto the cell body.
There, the incoming information from all neighbouring cells is combines. The many branches of the dendrites can receive input from 1000 or more neighbouring neurons. The surface of the cell body also has receptor areas that can be directly stimulated by other neurons. All parts of a neuron are covered by a cell membrane that controls the exchange of chemical substances between the inside and outside of the cell. These exchanges play a critical role in the electrical activities of nerve cells
29
What is an axon?
Extending from one side of the cell body is a single axon, which conducts electrical impulses away from the cell body to other neurons, muscles or glands. The axon branches out at its end to form a number of axon terminals - as many as several hundred in some cases. Each axon terminal may connect with dendrites from numerous neurons, making it possible for a single neuron to pass messages to many thousands of other neurons.
Given the structure of the dendrites and axons, it is easy to see how there can be trillions of interconnections in the brain, making it capable of performing the complex activities that are of interest to psychologists.
30
What 3 basic steps does nerve activation involve?
1) When not involved in creating impulses the neuron maintains an electrical resting potential through the distribution of positively and negatively charged chemical ions inside and outside the neuron
2) When stimulated by other neurons, a flow of ions in and out through the cell membrane depolarizes and reverses the electrical charge of the resting potential, producing an action potential, or neural impulse
3) The resting potential is again restored
31
What are neurons surrounded by? What does it do?
By body fluids and separated from this liquid environment by a cell membrane. This cell membrane is a bit like a selective sieve allowing certain substances in the body fluid to pass through ion channels into the cell, while refusing or limiting passage to other substances
32
How does the chemical environment inside the neuron differ from its external environment?
It differs in significant ways, and the process whereby a nerve impulse is created involves the exchange of electrically charged atoms called ions. In the salty fluid outside the neuron are positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). Inside the neurons are large negatively charged protein molecules (anions, or A-) and positively charged potassium ions (K+).
The cell membrane actively maintains a high concentration of Na+ ions in the fluid outside the cell via an ion pump, and this results in an uneven distribution of positive and negative ions that creates an electrical charge difference across the membrane with the interior of the cell negatively charged, and the exterior positively charged.
This difference of 70 millivolts (mV) is called the neuron's resting potential. In a way, calling this a 'resting' potential contradicts the fact that the cell actively expends energy in maintaining this balance of charge (also known as a state of polarization). This resting potential sets the stage, allowing the neuron to fire off a communicative impulse - an action potential - when required
33
What is the resting potential?
Internal difference of around 70 millivolts (mV)
34
What is the action potential?
An electrical shift across the neural membrane, which lasts about a millisecond (1/1000 of a second) and propagates electrical signals down an axon
35
How is an action potential brought about?
Hodgkin and Huxley found that the key mechanism underlying an action potential was the work of sodium and potassium ion channels in the cell membrane. In a resting state, the neuron's sodium and potassium channels are closed and the concentration of Na+ ions is 10x higher outside the neuron than inside it. But when a neuron is stimulates sufficiently, nearby sodium channels open. Attracted by the negative protein ions inside, positively charged sodium ions flood into the axon, creating a state of depolarisation. In an instant, the interior now becomes positive in relation to the outside, creating the action potential.
In a reflex action to restore the resting potential, the cell closes its sodium channels, and positively charged potassium ions flow out through their channels, restoring the negative resting potential. Eventually the excess sodium ions flow out of the neuron, and the escaped potassium ions are recovered. The resulting voltage can be traced in the resting potential graph.
36
What is the absolute refractory period and what does it do?
Once an action potential occurs at any point on the membrane, its effects spread to the adjacent sodium channels, and the action potential flows down the length of the axon to the axon terminals. Immediately after an impulse passes a point along the axon, however, there is a recovery period as the K+ ions flow out of the interior. During this absolute refractory period, the membrane is not excitable and cannot discharge another impulse. This places an upper limit on the rate at which nerve impulses can occur. In humans, the limit seems to be about 300 impulses per second. The absolute refractory period also prevents the action potential from travelling back down the axon the way it has come.
37
What is the 'all-or-nothing' law?
Action potentials occur at a uniform and maximum intensity, or they do not occur at all. Like firing a gun, which requires that a certain amount of pressure to be placed on the trigger the negative potential inside the axon has to be changed from -70 millivolts to about -50 millivolts (the action potential threshold) by the influx of sodium ions into the axon for the action potential to be triggered. Changes in the negative resting potential that do not reach the -50 millivolt action potential threshold are called graded potentials. Under certain circumstances, graded potentials caused by several neurons can add up to trigger an action potential in a post-synaptic neuron
38
What are graded potentials?
Changes in the negative resting potential that do not reach the -50 millivolt action potential threshold
39
How do drugs influence nerve impulses?
For a neuron to function properly, sodium and potassium ions must enter and leave the membrane at just the right rate. Drugs that alter this transit system can decrease or prevent neural functioning. For example, local anaesthetics such as Novocain and Xylocaine attach themselves to the sodium channels, stopping the flow of sodium ions into the neurons. This is how these anaesthetics stop pain impulses from being sent by neurons.
40
What is a myelin sheath?
A whitish, fatty insulation layer derived from glial cells during development which covers many (but not all)axons. Myelin is what makes the white matter white
41
What does the myelin sheath do?
Because the myelin sheath is interrupted at regular intervals by the nodes of Ranvier, where the myelin is either extremely thin or absent, myelinated axons look a bit like sausages placed end to end. In axons lacking the myelin sheath, the action potential travels down the axon length in a point-to-point fashion like a burning fuse. But in myelinated axons, the nodes of Ranvier are close enough to one another so that depolarization at one node can activate the next node, allowing electrical conduction to jump from node to node at higher speed
42
Where are myelin sheaths found?
The myelin sheath is most commonly found in the nervous systems of higher animals. In many neurons, the myelin sheath is not completely formed until sometime after birth, and in humans continues to develop even into late childhood and adolescence. The resulting efficiency of neural transmission is partly responsible for some of the gains that infants and children exhibit in muscular coordination and cognitive functioning as they grow older.
43
What does damage to myelin do?
It can have tragic effects. In people afflicted with multiple sclerosis, the person's own immune system attacks the myelin sheath, disrupting the delicate timing of nerve impulses to the muscles. The result is increasingly jerky and uncoordinated movements and, in the final stages, paralysis
44
What is the synaptic cleft?
A tiny gap between the axon terminal and the next neuron
45
What do synapses do?
They are a crucial element in the function of the nervous system as they determine how information is passed through the nervous system. Changes in synaptic connectivity between neurones leads to learning and the formation of memories. Changes in synaptic connectivity in early life have important influences on psychological development. Increases in synapses between neurons, and concurrent pruning back of connections during infancy are thought to play important roles in the development of many of the psychological functions we possess as adults
46
What are neurotransmitters?
Chemical substances that carry messages across the synaptic cleft to other neurons, muscles or glands.
47
What are synaptic vesicles?
Chambers within the axon terminals
48
What are receptor sites?
Large protein molecules embedded in the receiving neuron's cell membrane
49
What happens when action potentials arrive at the axon terminals?
Neurones produce neurotransmitters. This chemical communication involves 5 steps: synthesis, storage, release, binding and deactivation.
In the synthesis stage, the transmitter molecules are formed inside the neuron. The molecules are then stored in synaptic vesicles. When an action potential comes down the axon, these vesicles move to the surface of the axon terminal and the molecules are released into the fluid-filled space between the axon of the presynaptic (sending) neuron and the membrane of the postsynaptic (receiving) neuron. The molecules cross the synaptic cleft and bind themselves to receptor sites, large protein molecules embedded in the receiving neuron's cell membrane. Each receptor site has a specially shaped surface that fits a specific transmitter molecule, just as a lock accommodates a single key
50
What happens when a transmitter molecule binds to a receptor site?
A chemical reaction occurs and has two possible effects on the receiving neuron. When an excitatory transmitter is at work, the chemical reaction causes the postsynaptic neuron's sodium channels to open. As sodium ions flood into the cell and depolarize I, they create either a graded potential or an action potential. An inhibitory neurotransmitter will do the opposite. It may cause positive potassium ions to flow out of the neuron or negative chloride ions from the exterior to flow into it through chloride channels in the membrane, increasing the neuron's negative potential and making it harder to fire the neuron. The action of an inhibitory neurotransmitter from one presynaptic neuron may prevent the postsynaptic neuron from firing an action potential even if it is receiving excitatory stimulation from other neurons at the same time
51
What happens after a neurotransmitter molecule binds to its receptor?
It continues to excite or inhibit the neuron until it is deactivated, or shut off. Some transmitter molecules are deactivated by other chemicals located in the synaptic cleft that breaks them down into their chemical components. In other instances, the deactivation mechanism is re-uptake, in which the transmitter molecules are taken back into the presynaptic axon terminals. Some antidepressant medications inhibit re-uptake of the excitatory transmitter serotonin, allowing serotonin to continue to excite neurons and thereby reduce depression
52
What is re-uptake?
The transmitter molecules are taken back into the presynaptic axon terminals
53
How are transmitter systems specialized?
There is only one kind of electricity, but there are many shapes that can be assumed by transmitter molecules. Because the various systems in the rain recognise only certain chemical messengers, they are immune to neurotransmitters produced by different systems.
There are many different neurotransmitter substances, some of which can coexist within the same neuron. A given neuron may use one transmitter at one synapse and a different transmitter at another synapse. Moreover, different transmitters can be found within the same axon terminal or in the same synapse, adding another layer of complexity. Each substance has specific excitatory or inhibitory effect on certain neurons. Some neurotransmitters (e.g. noradrenaline) can have either excitatory or inhibitory effects, depending on which receptor sites they bind to
54
What is acetylcholine (ACh)?
A neurotransmitter involved in muscle activity and memory
55
What happens if there is an underproduction of ACh?
Underproduction on ACh is an important factor in Alzheimer's disease which is a neurodegenerative disorder which is the most common cause of dementia in adults over 65 years of age. The most well-known impairments in Alzheimer's disease are associated with memory, but it also leads to difficulties in speech and movement. Reductions in ACh weaken or deactivate neural circuitry that stores memories, creating profound memory impairments. ACh is also an excitatory transmitter at the synapses where neurons activate muscle cells, helping to account for some of motor impairments found in Alzheimer's disease
56
What can drugs that block the action of ACh do?
They can prevent muscle activation and cause paralysis. One example occurs in botulism, a serious type of food poisoning that can result from improperly canned food. the toxin formed by the botulinum bacteria blocks the release of ACh from the axon terminal, resulting in a potentially fatal paralysis of the muscles, including those of the respiratory system
57
What is the botulinum bacteria?
A toxin-forming bacteria, a mild form of which is known commonly as botox
58
What happens regarding ACh with a black widow spider bite?
The spiders venom triggers a torrent of ACh, resulting in violent muscle contractions, convulsions and possible death
59
What are neuromodulators?
They have a more widespread and generalized influence on synaptic transmission
60
What do neuromodulators do?
These substances circulate through the brain and either increase or decrease (i.e. modulate) the sensitivity of thousands, perhaps millions, of neurons to their specific transmitters. Endorphins are neuromodulators that travel through the brain's circulatory system and inhibit pain transmission while enhancing neural activity that produces pleasurable feelings. Other neuromodulators play important roles in a range of functions including eating, sleeping and coping with stress
61
What are psychoactive drugs?
Chemicals that produce alterations in consciousness, emotion and behaviour
62
What is an agonist?
A drug that increases the activity of a neurotransmitter
63
What is an antagonist?
A drug that inhibits or decreases the action of a neurotransmitter
64
What is neuropsychology?
The study of the function of the brain by investigating the effects of brain damage on mental functions
The study of effects of brain damage on psychological functioning, often in the form of individual case studies, has been one of the most productive methods for understanding the brain basis of psychological processes
65
What are neuropsychological tests?
Neuropsychologists use a variety of neuropsychological tests to measure verbal and non-verbal behaviours of people who may have suffered brain damage through accident or disease. As well as providing diagnostic tools, these tests are also important research tools.
66
What can be found through studying patterns of impairment and sparing of function on neuropsychological tests?
Neuropsychologists can draw inferences about how brain functions are related to one another in the brain. An important concept here is that of dissociation of function
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What is dissociation?
Put very simply, dissociation is a difference in performance between two tasks. For instance, if a patient or a group of patients with damage to a particular part of the brain performs poorly on a verbal dexterity but well on a comprehension then this provides some evidence that the damaged area of the brain is involved in verbal dexterity, but not comprehension. This kind of evidence is called a single dissociation
68
What is the issue with single dissociation?
Is that the pattern of findings could also be explained by appealing to differences in the difficulties of the two tasks. If the brain damage under investigation has more generally disrupted cognitive performance, giving the patient more general problems with attention or concentration, then they are more likely to show most impairment o the more difficult task. So, if impairment could explain the single dissociation without us needing to say that verbal dexterity and comprehension are separable functions sub-served by different parts of the brain
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What is double dissociation?
Stronger evidence of separation of function comes from double dissociation. In a double dissociation, we see a pattern in which a patient is impaired on task A but spared on task B, whereas a second patient is impaired on task B but spared on task A. When we have a double dissociation like this, we can say much more confidently that the differences seen are due to the fact that these two tasks are sub-served by functionally separate systems in the brain.
70
What is, perhaps, the most famous example of double dissociation?
Is between Broca's and Wernicke's aphasias. they were two early neuropsychologists working at the end of the 19th century. On the basis of brain observations of brain damage, known respectively as Broca's area and Wernicke's area.
71
What happens when there is damage to the Wernicke's area in the temporal lobe of the brain?
Typically leaves patients unable to understand written or spoken speech. Scott Moss, a psychologist, who suffered temporary aphasia from a left-hemisphere stroke described his experience: 'I recollect trying to read the headlines of the Chicago Tribune but they didn't make any sense to me at all. I didn't have any difficulty focussing, it was simply that the words individually or in combination did not have meaning.' However, patients with Wernicke's aphasia can typically produce speech, but due to the deficit in comprehension that speech tends to be jumbled
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What is Wernicke's aphasia?
Results from damage in the temporal lobe, and is primarily manifested as difficulties with speech comprehension
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What happens when there is damage to the Broca's area in the frontal lobe of the brain?
Can lead to the opposite pattern of damage to the Wernicke's area. Whereas patients with Broca's aphasia are usually able to understand speech, their difficulties are in expressing speech with words and sentences.
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What is Broca's aphasia?
Results from damage in the frontal lobe and is primarily manifested as difficulties with the production of speech
75
What is important to note about Broca's and Wernicke's aphasias?
It is important to bear in mind that the individual patients with Broca's and Wernicke's aphasias can vary in the extent to which they show pure impairments of production or comprehension, but this is a useful example for illustrating how evidence from brain damaged patients can help us understand how the brain underlies our different mental functions. Neuropsychological research not only helps us understand the functional architecture of the brain. It can also help greatly in targeted treatment or therapy
76
What are lesion studies in animals?
Experimental lesion studies with animals are another useful method of learning about the brain. Researchers can produce brain damage (lesions) in which specific nervous tissue is destroyed with electricity, with cold or heat, or with chemicals. They can also surgically remove some portion of the brain and study the consequences
77
How can the activity of single neurons or small groups of neurons be measured?
By inserting small electrodes in particular areas of the brain. Occasionally, it is possible to d this kind of research in human, usually when a participant is undergoing investigative surgery for epilepsy. However, the majority of such studies are conducted with animals. Some of the most important advances in our understanding of how neurons work together to underpin perceptual and cognitive functions have come from such animal studies. For instance, in 1981, the neurophysiologists Hubel and Wiesel received the Nobel Prize for their work on how neurons in visual areas of the brain respond to different aspects of the visual world
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How can the activity of much larger groups of neurons be measures?
We can record neural activity from the surface of the scalp. Electroencephalography (EEG) measures the activity of large groups of neurons through a series of electrodes placed on the scalp. Although the EEG is a rather non-specific measure that taps the electrical activity of thousands of neurons in many parts of the brain, specific EEG patterns correspond to certain states of consciousness, such as wakefulness and sleep.
This method has its advantages because it is possible to record the responses of large groups of neurons without an invasive procedure.
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What are EEGs?
Electroencephalography measures the activity of large groups of neurons through a series of large electrodes placed on the scalp
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What are MRIs?
In magnetic resonance imaging (MRI) a strong magnetic field is passed through the brain and pulsed on and off. This oscillating magnetic field causes the molecules and atoms in the brain (or any tissue) to respond. When the magnetic field is shut off, the molecules in the brain emit a radio signal which is then detected and mapped to provide images of the tissue
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What do MRIs create?
Images based on how atoms in living tissue respond to a magnetic pulse delivered by the device
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What are DTIs?
A more recent method using MRIs is diffusion tensor imagine (DTS). It measures how water molecules diffuse in tissue. In the brain water molecules are not free to move in any direction because of the shapes of cells and structures which they inhabit. This means that we can get information about how structures and pathways or tracts in the brain are aligns. This has been particularly useful for providing pictures of how white matter tracts are arrayed in the brain, telling us about how the brain is structurally connected
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What do DTIs measure?
How water molecules diffuse in tissue
84
What are fMRIs?
A particularly important advance in MRI technology is functional MRI (fMRI). fMRI makes use of the fact that oxygenated and deoxygenated blood respond differently to the magnetic fields used with MRI scans. When there is neural activity more oxygenated blood is sent to that particular part of the brain. fMRI researchers thus investigate where the highest concentrations of oxygenated blood are being sent in the brain at any one time, and infer on that basis which parts of the brain are most active when a participant is undertaking a particular task. If the patient is performing a reasoning task, for example a researcher can tell from the fMRI which parts of the brain are most active during reasoning.
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What can fMRIs produce?
Can produce pictures of blood flow in the brain taken less than a second apart
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What are PET scans?
Positron-emission tomography (PET) scans have provided another way of measuring where blood flows to in the brain. Glucose, a natural sugar, is the major nutrient of neurons, so when neurons are active, they consume more glucose. To prepare a patient for a PET scan, a radioactive form of glucose is injected into the bloodstream and travels to the brain, where it circulates in the blood supply. The PET scan measures the energy emitted by the radioactive substance, and can thus map put which parts of the brain are most active.
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What do PET scans measure?
Brain activity, including metabolism, blood flow and neurotransmitter activity
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What is a disadvantage of PET scans?
Involves the injection of radioactive isotopes which can be harmful is applied frequently. This is one of the reasons why fMRI is a more popular method for imagine brain activity.
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What is an advantage of PET scans?
It is possible to use radioactive isotopes to label particular neurotransmitters. This means that PET is still an important method for investigating the role of particular neurotransmitters in brain function
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What are fNIRS?
Functional near-infrared spectroscopy (fNIRS) is a relatively new method for investigating brain function. It involves shining a particular kind of light (near- infrared light) into the brain and measuring the ways in which it is reflected back. This method is completely non-invasive as near-infrared light (although we cannot see it) is naturally occurring and able to permeate biological tissue, In fact near-infrared light is likely shining into your brain right now. Because oxygenated and deoxygenated blood absorb near-infrared light to different extents it is possible to use fNRIS in a similar way to fMRI, measuring he signatures of blood flow to determine which parts of the brain are the most active.
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What can fNRIS tell us?
By shining near-infrared light into the brain and measuring the ways in which it is reflected, fNRIS can tell us about which parts of the brain are using most oxygen
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What is a disadvantage of fNRIS?
fNRIS is a little limited in comparison to fMRI as it gives less precise maps of the brain are it can only really tell us about blood flow in areas close to the scalp (as near-infrared only illuminates a few centimetres into the brain)
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What are the advantages of fNRIS?
Firstly, it is a relatively inexpensive technique to use by comparison with fMRI.
Secondly, whereas fMRI simply does not work if the participant moves, with fNRIS it is possible to image the brain of someone who is moving around and acting on their environment. This makes it particularly useful for examining the neural basis of motor behaviours, and also makes it very handy for using with participants who do not usually sit still e.g. infants
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What is an alternative for measuring the activity of neurons?
Stimulate them and see what happens as a response.
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What is the importance of brain stimulation techniques?
That they can show us more directly about what processes brain activities drive. If we are gathering EEG or observing fMRI data while a person engages in a particular task, we are always simply looking at hat kinds of neural activity are correlated with a particular behaviour. It is more difficult to determine whether the activity we are observing actually causes the behaviours of interest, To look at causes, we can intervene directly in brain processes and measure the outcomes.
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How are brain stimulation studies carried out experimentally?
With animals and chemical simulation, a tiny tube, or cannula, is inserted into a precise area of the brain so that chemicals, including neurotransmitters, can be delivered directly and their effects on behaviour studied. A specific region of the brain can also be stimulated by a mild electric current. Electrodes can be permanently implanted so that the region of interest can be stimulated repeatedly. Some electrodes are so tiny that they can stimulate individual neurons.
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How can electrical-stimulation studies be applied in humans?
Often when electrodes are implanted in order to evaluate patients in advance of treatment for epilepsy. In the 1930s-50s, a neurosurgeon (Penfield) conducted several investigations on the effects of brain stimulation in epilepsy patients who were unconscious by locally anaesthetized on the operating table. From these studies, he was able to make precise maps of the function of somatosensory cortex, the part of the brain involved in sensing touches. When he stimulated a particular part of somatosensory cortex the patients reported where they felt touch sensations. he found that the whole body was mapped out over the somatosensory cortex in a regular organisation of limbs and body parts.
In another, more recent, study of this type, placement of electrodes on a specific region of the brain's outer surface above the right ear produced a surprising effect. A patient experiences herself as floating in the air above her body. Neuroscientists have argued that this area of the brain is intimately involved in the neural basis of bodily experiences
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What is TMS?
Transcranial magnetic stimulation (TMS) offers researchers a way of stimulating the brain in a non-invasive way. TMS researchers place an electromagnetic coil over the brain of a participant. A large electrical current is passed through the coil, and this gives rise to a focussed magnetic field which in turn induces an electrical current in the neural circuits of the brain.
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What is the main way in which TMS is used?
In research in order to introduce temporary lesions in a kind of 'virtual neuropsychology' mimicking the effects of focal brain damage. TMS can temporarily disrupt function in the area of the brain over which it is placed, and so researchers can measure the effects of these temporary lesions on mental processes. For instance, applying TMS above part of the temporal cortex disrupts picture naming. Applying TMS over a brain area known as the interparietal sulcus impairs people's ability to make judgements about numbers.
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How does TMS work?
Electrical stimulation of a targeted part of the brain via magnetic pulses sent from an electromagnetic coil
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What is TDCS?
Transcranial direct current stimulation. Electrical stimulation of the brain by applying a low current to the scalp
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How can enhancing mental performance be studied?
More recently, researchers have begun investigating how brain stimulation can actually enhance mental performance. It has been found that both TMS and another method which is gaining interest called transcranial direct current stimulation (TDCS) can enhance mental processes and learning. For instance, researchers recently shows that TDCS over an area of the brain called the temporoparietal junction (TPJ) improves people's ability to take different social perspectives. The application of these kinds of methods to treating psychological illnesses such as depression is garnering a lot of interest at present
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What do the structures at the brains core do?
Govern the basic physiological functions that keep us alive, such as breathing and heart rate.
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What do the newer systems in the brain do?
Involve progressively complex functions - sensing, emoting, wanting, thinking and reasoning.
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What is the hindbrain?
The lowest and most primitive level of the brain
As the spinal cord enters the brain, it enlarges to form the structures that compose part of the stalk-like brain stem, which also includes the midbrain. Attached to the hindbrain part of the brain stem id the other major portion of the hindbrain, the cerebellum.
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What do the structures of the brain stem do?
They support vital life functions. Included are the medulla and the pons.
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What is the medulla?
The 1.5-inch-long (3.8cm) medulla is the first structure above the spinal cord. Well developed at birth, the medulla plays an important role in vital body functions such as heart rate and respiration. Because of your medulla, these functions occur automatically
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What does damage to the medulla usually result in?
Death or, at best, the need to be maintained on life-support systems.
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What happens when medulla activity is suppressed?
Suppression of medulla activity can occur at high levels of alcohol intoxication, resulting in death by heart or respiratory failure
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What does the medulla also do with sensory and motor nerve tracts?
he medulla is also a two-way thoroughfare for all the sensory and motor nerve tracts coming up from the spinal cord and descending from the brain. Most of these tracts cross over within the medulla, so the left side of the brain receives sensory input from and exerts motor control over the right side of the body, and the right side of the brain serves the left side of the body. Why this crossover occurs is one of the unresolved mysteries of brain function.
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What is the pons?
The pons (Latin for 'bridge')lies just above the medulla and acts as a relay or sensory information between the cerebral cortex and the cerebellum. The pons also has clusters of neurons that help regulate sleep. Like the medulla, the pons helps control vital functions, especially respiration, and damage to it can produce death
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What is the cerebellum?
Attached to the rear of the brain stem, the cerebellum ('little brain' in Latin) does indeed look like a miniature brain. Its wrinkled cortex, or covering, consists mainly of grey cell bodies (grey matter). The cerebellum is concerned primarily with muscular movement coordination, but it also plays a role in learning and memory.
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Where are specific motor movements initiated?
In higher brain centres, but their timing and coordination depend on the cerebellum.
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What does the cerebellum regulate?
Regulates complex, rapidly changing movements that require precise timing, such as those of a ballet or a classical pianist. Within the animal kingdom, cats have an especially well-developed cerebellum, helping to account for their ability to move gracefully and precisely.
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How can the cerebellum be linked to sobriety tests?
The motor-control functions of the cerebellum are easily disrupted by alcohol producing the coordination difficulties that some police forces look for in roadside sobriety tests. Intoxicated people may be unable to walk in a straight line or touch their nose with their index finger.
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What does physical damage to the cerebellum result in?
Severe motor disturbances characterised by jerky, uncoordinated movements, as well as an inability to perform habitual movements such as walking
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What is the midbrain?
Lying just above the hindbrain, the midbrain contains clusters of sensory and motor neurons. The sensory portion of the midbrain contains important relay centres for the visual and auditory systems. here, nerve impulses from the eyes and ears are organised and sent to forebrain structures involved in visual and auditory perception.
The midbrain also contains motor neurons that control eye movements. Some of the exotic named structures in the midbrain include the reticular formation, the tectum (including the superior and inferior colliculi) and the substantia nigra
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What is the reticular formation known as?
The brain's gatekeeper
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What is the reticular formation?
Buried within the midbrain is a finger-shaped structure that extends from the hindbrain up into the lower portions of the forebrain. This structure received its name from its resemblance under a microscope to a reticulum or net. The reticular formation acts as a kind of sentry, both alerting higher centres of the brain that messages are coming and then either blocking those messaged or allowing them to got forward. It has an ascending part, which sends input into higher regions of the brain to alert it, and a descending portion, through which higher brain centres can either admit or block out sensory input
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What does the reticular formation play a central role in?
In consciousness, sleep and attention. Without reticular stimulation of higher brain regions, sensory messages do not register in conscious awareness even though the nerve impulses may reach the appropriate higher areas of the brain. It is as if the brain is not awake enough to notice them. In fact, some general anaesthetics work by deactivating neurons of the ascending reticular formation so that sensory impulses that ordinarily would be experienced as pain never register in the areas of the brain.
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How does the reticular formation influence wakefulness & attention?
Researchers discovered that electrical stimulation of different portions of the reticular formation can produce instant sleep in a wakeful cat and sudden wakefulness in a sleeping animal.
Attention is an active process during which only important or meaningful sensory inputs get through to out consciousness, Other inputs have to be toned down or completely blocked out or we would be overwhelmed by stimulation. the descending reticular formation plays an important part in this process, serving as a kind of gate through which some inputs are admitted while others are blocked out by signals coming down from higher brain centres
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What can damage to the reticular formation do?
Can produce a permanent coma
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What is the forebrain?
the most recently evolved part of the brain. Its major structure, the cerebrum, consists of two large hemispheres, a left side and a right side, that wrap around the brain stem as the two halves of a cut grapefruit might wrap around a large spoon. The outer portion of the forebrain has a thin covering, or cortex. Within the cerebrum are a number of other important forebrain structures buried in the central regions of the hemispheres
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What is the cerebrum?
The most superior part of the forebrain comprising the cerebral cortex and several more central structures
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What is the thalamus known as?
The brain's sensory switchboard
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What is the thalamus?
The thalamus is located above the midbrain. It resembles two small balls, one within each cerebral hemisphere. the thalamus has sometimes been likened to a switchboard that organises inputs from sensory organs and routes them to the appropriate areas of the brain. the visual, auditory and body senses (balance and equilibrium) all have major relay stations in the thalamus
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What happens when the functioning of the thalamus is disrupted?
Individuals would experience sensory confusion. Disrupted function of the thalamus has been implicated especially in schizophrenia, and stroke damage in the thalamus often gives rise to schizophrenia-like symptoms. It is possible that thalamic damage may lead to garbled sensory information being sent to the higher regions of the brain, creating the confusing sensory experiences and hallucinations reported by schizophrenia patients
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Define the thalamus ---
has sometimes been likened to a switchboard that organises inputs from sensory organs and routes them to the appropriate areas of the brain
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What is the hypothalamus?
The hypothalamus (literally 'under the thalamus') consists of tiny groups of neuron cell bodies that lie at the base of the brain, above the roof of the mouth. The hypothalamus plays a major role in many aspects of motivation and emotion, including sexual behaviour, temperature regulation, sleeping, eating, drinking and aggression. (involved in experiences of pleasure)
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What happens if the hypothalamus is damaged?
Damage to the hypothalamus can disrupt sexual behaviour, temperature regulation, sleeping, eating, drinking and aggression. For example destruction to one area of a male's hypothalamus results in a complete loss of sex drive; damage to another portion produces an overwhelming urge to eat, resulting in extreme obesity
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With what does the hypothalamus have important connections with?
the endocrine system, the body's collection off hormone-producing glands. Through its connection with the nearby pituitary gland (the master gland that exerts control over the other glands in the endocrine system), the hypothalamus directly controls many hormonal secretions that regulate sexual development and sexual behaviour, metabolism ad reactions to stress
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What is the limbic system?
The limbic system, a set of structures lying deep within the cerebral hemispheres, helps coordinate behaviours needed to satisfy motivational and emotional urges that arise in the hypothalamus. It is also involved in memory
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What are the two key structures in the limbic system?
The hippocampus and the amygdala
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What is the hippocampus?
The hippocampus is involved in forming and retrieving memories.
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What happens if the hippocampus is damaged?
Can result in severe memory impairment for recent events
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What is the amygdala?
(From the Greek word for 'almond') is involved in emotional behaviours, particularly those linked to aggression and fear. Electrically stimulating certain areas of the amygdala causes animals to snarl and assume aggressive postures, whereas stimulation of other areas results in a fearful inability to respond aggressively., even in self-defense. For example, a normally aggressive and hungry cat will cower in fear from a tiny mouse placed in its cage. The amygdala can also produce emotional responses without the higher centres of the brain 'knowing' that we are emotionally aroused, providing a possible explanation for unconscious emotional responses
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Why do the amygdala and hippocampus need to interact?
the amygdala is a key part of a larger control system for anger and anger that also involves other brain regions. It has important interconnections with the hippocampus and amygdala stimulation is important in the hippocampus' creation of emotional memories. Without amygdala activity, emotional memories are not well established
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What can certain drugs do to the limbic system?
Certain drugs, such as cocaine and marijuana, seem to induce pleasure by stimulating limbic reward areas that use dopamine as their neurotransmitter
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What is the cerebral cortex known as?
Crown of the brain
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What is the cerebral cortex?
The most recently part of the forebrain which is a 0.63cm thick sheet, consisting primarily of grey matter (i.e. unmyelinated cell bodies). This is the outermost layer of the human brain.
Fish and amphibians have no cerebral cortex, and the progression from more primitive to more advanced mammals is marked by a dramatic increase in the proportion of cortical tissue. In humans, the cortex and its underlying white matter constitutes 80% of brain tissue
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How does the structure of the cerebral cortex aid its function?
Because the cortex is wrinkled and convoluted, like a waddled-up piece of paper, a great amount of cortical tissue is compressed into a relatively small space inside the skull. If we could remove the cortex and smooth it out, the tissue would cover an area roughly the size of a pillowcase. Perhaps 75% of the cortex's total surface area lies within its fissures, the inward folds of the cortex which are not visible on the surface.
Three of these fissures (also known as sulci) are important landmarks. One large fissure runs lengthwise across the top of the brain, dividing it into a right and left hemisphere. This is called the medial longitudinal fissure. Within each hemisphere the central fissure divides the cerebrum into a front (anterior) and rear (posterior) halves., and a third fissure, the sylvian fissure, runs from front to rear along the side of each hemisphere. On the basis of these landmarks, neurologists have divided each hemisphere into four lobes: frontal, parietal, occipital and temporal. A fist made with your right hand (with the side of your thumb facing you) can serve as a rough orientation to these lobes. The bend in your fingers represents the frontal lobe, your knuckles the parietal lobe, your wrist are the occipital lobe, and your thumb the temporal lobe of the left hemisphere
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What is the motor cortex?
The motor cortex controls the 600 or more muscles involved in voluntary body movements.
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Where is the motor cortex found?
It lies at the rear of the frontal lobs adjacent to the central fissure. Because the nerve tracts from the motor cortex cross over at the level of the medulla, each hemisphere governs movement on the opposite side of the body.
Specific body areas have different amount of cortex devoted to it depending on the complexity of movements that are carried out by the body part. For example, the amount of cortical tissue devoted to your fingers is far greater than that devoted to your torso, even though your torso is much larger. If we electrically stimulate a particular point on the motor cortex, movements occur in the muscles governed by that part of the cortex
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What would damage to the motor cortex?
Severe damage to the right motor cortex would produce paralysis in the left side of the body.
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What are the sensory cortices?
Specific areas of the cortex receive input from our sensory receptors. With the exception of taste and smell, at least one specific area in the cortex has been identified for each of the senses
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What is the somatosensory cortex?
Receives sensory input that gives rise to our sensations of heat, touch and cold, and to our senses of balance and body movement (kinaesthesis). It lies at the front portion of the parietal lobe just behind the motor cortex, separated from the more anterior motor cortex by the central fissure. In a similar arrangement to the motor system, each side of the body sends sensory input to the opposite hemisphere.
The somatosensory area is basically organised in an upside-down fashion, with the feet being represented near the top of the brain. Likewise, the amount of cortex devoted to each body area us directly proportional to that region's sensory sensitivity. The organisation of the sensory cortex is such that the body structures it serves lie side by side with those in the motor cortex, an arrangement that enhances sensory-motor interactions in the same body area
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How are the senses of hearing and sight represented in the cortex? And how are messages of these sent?
They are represented well. The primary auditory cortex lies on the surface of the temporal lobe at the side of each hemisphere. Each ear sends messages to the auditory areas of both hemispheres, so the loss of one temporal lobe has little effect on hearing. The primary visual cortex lies at the rear of the occipital lobe. Here, messages from the eyes are analysed, integrates and translated into sight. As in the auditory system, each eye sends input to both hemispheres
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How are some neurons tuned to respond to particular aspects of the sensory stimulus within each sensory area?
They are sensitive to particular aspects of the environment. Thus certain cells in the visual cortex fire only when we look at a particular kind of stimulus such as a vertical line or a corner. In the auditory cortex, some neurons fire only in response to high tones whereas others respond only to tones having some other specific frequency. Most of these neuronal responses are present at birth, suggesting that we are pre-wired to perceive many aspects of our sensory environment. nonetheless, the sensory cortices, like other parts of the brain, is also sensitive to experience, E.g. when people learn to read Braille, the area in the somatosensory cortex that receives input from the fingertips increases in size, making the person more sensitive to the tiny sets of raised dots
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What is the association cortex?
The association cortices are involved in many important mental functions, including perception, language and thought. These areas are sometimes referred to as 'silent areas' because electrically stimulating them does not give rise to either sensory experiences or motor responses
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What can damage to specific parts of the association cortex do?
Can cause disruption or loss of functions such as speech, understanding, thinking and problem-solving.
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What changes about the association cortex as we move up the brain ladder from lower animals to human beings?
the amount of association cortex increases dramatically. It constitutes about 75% of the human cerebral cortex which presumably accounts for the human tendency to engage in more cognitive behaviours. One scientist has described our mass of association cortex as 'evolution's missing link'. he suggests that its flexibility and learning capacity have allowed us to acquire new mental skills specific to our human way of life, such as reading and mathematics, far more quickly than could have occurred through natural-selection alone
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What is an example of the importance of the association cortex?
The importance of the association cortex is demonstrated in people who suffer from agnosia, the inability to identify familiar objects. One such case is described by the neurologist Oliver Sacks - The Man Who Mistook His Wife For a Hat (The patient has suffered brain damage that left him unable to connect the information sent to the visual cortex with information stored in other cortical areas that concerned the nature of objects. The associative neurons responsible for linking the two types of information no longer served him)
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Define the association cortex ---
It is involved in many important mental functions, including perception, language and thought
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Where do some neuroscientists suggest that the entire period of human evolutionary existence could be termed?
The frontal lobe. This brain region hardly exists in mammals such as mice and rats. The frontal lobes compose about 3.5% of the cerebral cortex in the cat, 7% in the dog, and 17% in the chimpanzee. In a human, the frontal lobes constitute 29% of the cortex.
The frontal lobes - the site of such human qualities such as self-awareness, planning, initiative and responsibility - are certainly the most mysterious and least understood parts of the brain
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What does frontal lobe damage result in?
Results in not so much a loss of intellectual abilities as in an inability to plan and carry out a sequence of actions, even when patients can verbalise what they should do. this can result in an inability to correct actions that are clearly erroneous and self-defeating .
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What is the frontal cortex also involved in?
Emotional experience. In people with normal brains, PET scans show increased activity in the frontal cortex when people are experiencing feelings of happiness, sadness or disgust. In contrast, patients with frontal lobe damage often exhibit attitudes of apathy and lack of concern. They simply do not seem to care about anything.
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What part of the frontal lobe has received increasing attention in recent years?
The prefrontal cortex, located just behind the forehead, is the seat of the so-called executive functions.
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What are executive functions?
They are mental strategic planning and impulse control - which allow people to direct their behaviour in an adaptive fashion.
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What do people with prefrontal cortex disorders seem?
They seem oblivious to the further consequences of their actions and seem to be governed only by immediate consequences.
A more ominous manifestation of prefrontal dysfunction - the capacity to kill - was recently discovered by researchers using PET technology.
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What connects the left and right vertebral hemispheres?
A broad white band of myelinated nerve fibres. The corpus callosum is a neural bridge consisting of white matter tracts that acts as a major communication link between the two hemispheres and allows them to function as a single unit. Despite the fact that they normally act in concert, there are important differences between the psychological functions of the two cerebral hemispheres
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What does lateralization refer to?
The relatively greater localisation of a function in one hemisphere or the other
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What was observed in people with brain damage to either the left or right hemisphere and what did this therefore show?
Suggested that for most people, verbal abilities and speech are localised in the left hemisphere, as are mathematical and logical abilities. When Broca's or Wernicke's speech areas in the left hemisphere are damaged, the result is aphasia, the partial or total loss of the ability to communicate. Depending on the location of the damage, the problem may lie in recognising the meaning of words, in communicating verbally with others, or in both functions.
We should note, however, that women are less likely to suffer aphasia when their left hemisphere is damaged, suggesting that for women, language is represented in both hemispheres to a greater extent than for men
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What happens when the right hemisphere is damaged?
the clinical picture is quite different. Language functions are not ordinarily affected, but the person has great difficulty perceiving spatial relations. A patient may have a hard time recognising faces and may even forget a well-travelled route or mistake a close relative. It appears that mental imagery, musical and artistic abilities, and the ability to perceive and understand spatial relations are primarily right-hemisphere functions.
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Apart from cognitive functions, how else do the left and right hemisphere differ?
In their links with positive and negative emotions. EEG studies have shown that the right hemisphere is relatively more active when negative emotions such as sadness and anger are being experienced. Positive emotions such as joy and happiness are accompanied by relatively greater left-hemisphere activation
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What happens if the corpus callosum is cut?
Visual input to only one hemisphere can be accomplished by projecting the stimulus to wither the right side of the visual field, in which case the image goes only to the left hemisphere, or to the left side of the visual field, which sends it to the right hemisphere
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What did Sperry's experiments on split-brain patients do and what did they show?
They focussed on a fixation point, a dot on the centre of a screen, while slides containing visual stimuli (words, pictures and so on) were flashed to the right or to the left side of the fixation point
Sperry found that when words were flashed to the right side of the visual field, resulting in these being sent to the language-rich left hemisphere, patients could verbally describe what they had seen. They could also write what they had seen with their right hand (which is controlled by the left hemisphere). However, if words were flashed to the left side of the visual field and sent on to the right hemisphere, the patients could not describe what they had seen on the screen. This pattern of findings indicates that the right hemisphere does not have well-developed verbal expressive abilities.
The inability to describe the stimuli verbally did not mean that the right hemisphere was incapable of recognising them. If a picture of an object was flashed to the right hemisphere and the left hand was allowed to feel different objects behind the screen, the person's hand would immediately select the brush. As long as the person continued to hold the brush in the left hand, sensory input about the object to the 'non-verbal' right hemisphere, the person was unable to name it. However, if the object was transferred to the right hand, the person could immediately name it. In other words, until the object was transferred to the right hand, the left hemisphere had no knowledge of what the right hemisphere was experiencing.
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Following Sperry's split-brain study, what has later research shown about the right hemisphere in regards to the left?
The right hemisphere's definite superiority over the left in the recognition of patterns. In one study, three split-brain patients were presented with photographs of similar looking faces projected in either the left or right visual fields. On each trial, they were asked to select the photo they had just seen in a set of 10 cards. In this task, the spatially oriented right hemisphere was far more accurate than the linguistic left hemisphere correctly identifying the photos. Apparently, the faces were too similar to one another to be differentiated very easily by left-hemisphere verbal descriptions, but the pattern-recognition abilities of the right hemisphere allowed discrimination among them. Split--brain research firmly established the different abilities of the two hemispheres
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What is neural plasticity?
Refers to the ability of neurons and brain areas and networks to change in structure and function
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What 2 aspects of neural plasticity are at the forefront of current research?
The effects of early experience on brain development and recovery from brain damage
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What research findings suggest that, despite brain development being programmed by complex gene commands, the environment in which we develop powerfully influences their expression?
1) Prematurely born human infants who were caressed and massaged on a regular basis showed faster neurological development than did those given normal care and human contact
2) The brains of rat pups raised in a stimulating environment weighed more and had larger neurons, more dendritic branched and greater concentration of acetylcholine (neurotransmitter involved in motor control & memory) than those of normally reared rats
3) MRI recordings have revealed that experienced violinists and other string-instrument players who do elaborate movements on the strings with their left hands had a larger right hemisphere somatosensory area devoted to these fingers than did non-musicians. the corresponding left hemisphere (right hand) cortical areas of the musicians and non-musicians did not differ. the earlier the musician has started playing, the greater the cortical differences
4) Some theorists believe that life stress has a similar negative effect on neuron formation in the brain, thereby causing or maintaining clinical depression. Antidepressant medications increase serotonin action in the brain, and serotonin increases neuron production in the brain
5) Cultural factors may affect brain development as well. E.g. the Chinese language uses complex pictorial images to represent objects or concepts. Because pictorial stimuli are processed in the right hemisphere, we might expect less left hemisphere lateralisation of language among speakers of Chinese than among people who speak English or other alphabet-based languages
6) Even your job may cause changes in your brain. A study showed that London taxi drivers, who are required to have an encyclopaedic knowledge of London's streets, have larger posterior hippocampuses than control participants. the hippocampus is known to play an important role in spatial navigation
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Why is it thought that young children can recover from brain damage more quickly and completely than adults?
The one to two year old child has about 50% more brain synapses than mature adults do. Some have argued that this greater ability of synapses in early life enables children to recover from brain damage more quickly and more completely than adults.
Some research suggests that the greater ability of synapses could make the brain more vulnerable, however
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What happens to weaker tor unused synapses?
They are pruned away with age, so that the brain loses some of its plasticity. Moreover, cell death is programmed into every neuron by its genes, and what some neuroscientists refer to as the neuron's 'suicide apparatus' is activated by a lack of stimulation from other neurons and many other factors which are not yet known.
As a result, adults have fewer synapses than children, despite their more advanced cognitive and motor capabilities. However, the remaining neurons form new connections in response to experiences and the formation of new memories. This plasticity, and ability to form new connections is extremely useful, but can be influenced. Nicotine, for example, has been shown to help concentration and cognition, and has been seen to show beneficial effects in those with Parkinson's disease, but findings have also been shown that is actually reduces the plasticity of cells in the frontal lobes
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What happens when nerve tissue is destroyed or neurons die as part of the ageing process?
Surviving neurons can restore functioning by modifying themselves either structurally or biochemically. They can alter their structure by sprouting large networks of dendrites or by extending axons from surviving neurons to form new synapses. Surviving neurons may also make up for the loss by increasing the volume of neurotransmitters they release. Moreover, research findings have disproved the long-standing assumption of brain scientists that dead neurons cannot be replaced in the mature brain. the production of new neurons in the nervous system is called neurogenesis
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What is neurogenesis?
The production of new neurons in the nervous system. It occurs in both the immature and the adult brain. In the adult brain, the birth of new cells has been established only in the hippocampus so far, but it may occur in other areas as well.
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What does cognitive neurogenomics refer to?
The genetic make-up of cognitive function. It typically involves the search for neuropsychological or biological markers for clinical disorders (i.e. ADHD, autism etc.) linked to known genetic patterns.
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What does one revolutionary neurogenesis technique involve?
The transplantation into the brain of neural stem cells, immature, 'uncommitted' cells that can mature into any type of neuron or glial cell needed by the brain.
These cells, found in both the developing and adult nervous systems, can be put into a liquid medium and injected directly into the brain. Once in the brain, they can travel to any of its regions, especially developing or degenerating areas. There they can detect defective or genetically impaired cells and somehow convert themselves into healthy forms of the defective cells. Stem cells have been successfully transplanted into the spinal cords of injured animals, where they have taken hold and organised themselves into neural networks. This success could hold an eventual ability to be able to heal the spinal cord.
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What can use of stem cells be used to treat?
Revolutionary treatments for diseases involving neural degeneration and dysfunction. These include Alzheimer's disease, multiple sclerosis, strokes, mental disorders and genetically based birth defects, all of which have serious psychological consequences.
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What is the endocrine system?
Consists of numerous hormone-secreting glands distributed throughout the body
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What are hormones?
Chemical messengers that are secreted from its glands into the bloodstreams
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What can endocrine messages trigger?
Responses in the brain, and mental processes within the brain can affect endocrine functioning. For example, negative thoughts about a stressful situation can quickly trigger the secretion of stress hormones within the body
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Why is the endocrine system much slower than the nervous system?
Because the delivery of its messages depends on the rate of blood flow. Nonetheless, hormones travel throughout the body in the bloodstream and can reach billions of individual cells. Thus, when the brain has important information to transmit, it has the choice of sending it quickly and directly in the form of nerve impulses to a relatively small number of neurons or indirectly by means of hormones to a large number of cells. Often both communication networks are used, resulting in both immediate and prolonged stimulation
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How do hormones influence our development, capacities and behaviour before we are born?
In the third to fourth month of pregnancy, genetically programmed releases of sex hormones in the foetus determine sex organ development, as well as differences in the structure and function of several parts of the nervous system, including the hypothalamus. One area of the hypothalamus affected in this manner continues to influence hormonal release later in life, such as the cyclic pattern or hormonal release during the female menstrual cycle.
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Aside from reproductive structures and sexual behaviours, what else can prenatal hormones affect?
A variety of other characteristics including sex differences in aggressiveness and longevity; males tend to be more aggressive than females and females live longer than men.
Prenatal hormones also produce differences in brain structures in males and females. Females have a greater density of neurons in language-relevant areas of the temporal lobe, which may contribute to the small overall superiority they manifest in verbal skills. They also tend to have a relatively larger corpus callosum than males, which may help account for the fact that language functions are less localised in the left hemisphere in females.
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What are adrenal glands?
Twin structures perched on top of the kidneys that serve, quite literally, as hormone factories, producing and secreting about 50 different hormones that regulate many metabolic processes within the brain and other parts of the body
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What do the adrenals produce/secrete?
produce the neurotransmitter dopamine, as well as several stress hormones. In an emergency, the adrenal glands are activated by the sympathetic branch of the autonomic nervous system. Stress hormones are then secreted into the bloodstream mobilizing the body's emergency response system. Because hormones remain in the bloodstream for some time, the action of these adrenal hormones is especially important under conditions of prolonged stress. If not for the long-term influence of hormones, the autonomic nervous system would have to produce a constant barrage of nerve impulses to the organs involved in responding to stress
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What other system do the nervous and endocrine system interact with?
The immune system
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What are antigens?
Foreign substances that trigger a biochemical response from the immune system
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How does the immune system have a memory?
Once it has encountered one of the millions of different antigens that enter the body, it will recognise the antigen immediately in the future and produce the biochemical weapons, or antibodies, needed to destroy it. This memory is the basis for developing vaccines to protect people and animals from some diseases; it is also the reason we normally catch diseases such as mumps and chicken pox only once in our lives. Unfortunately, though the memory may be perfect, our body's defences may not be. Some bacteria and viruses evolve so rapidly that they can change just enough over time to slip past the sentinels in our immune system and give us this year's cold or flu
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What has been dubbed the 'bodymind'?
The nervous, endocrine and immune systems are all part of a communications network that so completely underlies our every mental, emotional and physical action.
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What has been found, connecting the nervous and immune system?
Researchers found that electrical stimulation or destruction of certain sites in the hypothalamus and cerebral cortex resulted in immediate increases or decreases in immune-system activity. Conversely, activating the immune system by injecting antigens into the body resulted in increased electrical activity in several brain regions. Clearly, the nervous and immune systems were communicating with and influencing one another.
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What has been found, linking the nervous and immune system chemically?
Immune-system cells contain receptors keyed to specific neurotransmitter substances, meaning that the action of immune cells can be directly influenced by chemical messengers from the brain. An equally startling discovery was that immune cells can actually produce hormones and neurotransmitters, allowing them to directly influence the brain and endocrine system. In sum, the brain, endocrine glands and immune system form a complete communication loop, with having sensory and motor functions and each influencing and being influenced by one another
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What has research on psychological influences on the immune system showed?
A host of psychological factors that can increase or decrease immunity. For example, chronic stress, depression and pessimistic thinking reduce immune functioning, whereas stress management skills, an optimistic outlook, a sense of humour and social support help preserve immunity.
