Behavioural neuroscience

Question 1

What is Behavioural Neuroscience?

Answer 1

-A scientific study of the role of the central nervous system in behaviour
-Combines psychology and neuroscience
Allied disciplines:
Physiological psychology
Psychopharmacology
Neuropsychology
Psychophysiology
Cognitive neuroscience

Question 2

Historical limits to understanding the link between mind and brain

Answer 2

-Initially, heart was believed to be the seat of the mind
-Changes to our understanding of the brain were limited by:
religious or moral views
limited methods
reliance on chance discoveries (serendipity)
scientific conservatism

Question 3

The brain is proposed to control the body – Hippocrates 460 BCE

Answer 3

• Our brain is the command centre of body (not heart)
• Noted the behavioural effects of brain damage
• Dissection not allowed in Greece
• Observed anatomy through open wounds after traumatic head injury

Question 4

Nerves connect the brain to the body – Galen 130 CE

Answer 4

-Used vivisection to study anatomy of the nervous system
-Distinguished between sensory and motor nerves
-Proposed the idea of pneumata (‘spirits’)
Thought that animal spirits travelled through the hollow nerves to and from the ventricles
-No method or data to support or refute the pneumata theory

Question 5

Structure of the brain mapped in detail- Andreas Vesalius 1514 CE

Answer 5

• Revived dissection and vivisection after the Dark Ages
• Detailed drawings substantially advanced knowledge of brain structure but detailed anatomical understanding failed to illuminate brain function
• So the pneumata theory of animal spirits flowing through nerves persisted…

Question 6

Nerve signals are electrical (not fluid) - Luigi Galvani 1737

Answer 6

• Rejected the idea of animal spirits flowing through hollow nerves
• Found that an electrical charge applied to a frog’s leg made the muscle contract
• Suggested that nerves must be coated in fat to prevent electricity from leaking out

Question 7

The idea of a modular brain is proposed - Franz Joseph Gall 1758

Answer 7

• Influenced by physiognomy the art of ascribing personality characteristics to facial features
• Proposed that the brain was composed of several distinct ‘organs of thought’or faculties reflected by characteristic patterns of bumps on the skull
• skull maps could be used to “read” a person’s character
• Gall’s Phrenology is flawed
• but Gall introduced the important notion of cortical localisation of function

Question 8

The first solid evidence of brain modularity - Paul Broca 1861

Answer 8

-Paul Broca described a patient
unable to speak after damage to the left frontal lobe (Broca’s area)
-Normal chewing, comprehension

Question 9

Electrical stimulation of animal brains revealed precise localisation of cortical function

Answer 9

• In 1870, Fritsch & Hitzig (Germany) electrically stimulated part of the frontal cortex in dogs; induced contractions of specific muscles on the opposite side of the body
• Surgical removal of these ‘motor’ regions of cortex caused impairments of actions performed by the relevant limb

Question 10

Ablation studies

Answer 10

Ablation studies in non human primates reveals the hippocampus’ role in memory

Question 11

Role of CT and MRI

Answer 11

They both help to reveals brain structure

Question 12

Functional Magnetic Resonance Imaging (fMRI)

Answer 12

-Cognitive processes use energy
-The production of energy uses oxygen from hemoglobin (blood)
Oxygenated blood
-Weakly diamagnetic
-Doesn’t distort surrounding magnetic field
Deoxygenated blood
-Paramagnetic
-Distorts surrounding magnetic field
First observed by Seiji Ogawa in 1990
blood vessels became more visible as blood oxygen decreased
Basis for the BOLD effect

Question 13

The blood oxygen level dependent effect (BOLD)

Answer 13

reflects anticipated brain activity

-the flow of oxygenated blood is monitor through fMRI the see which part of the brain is active for a particular task

Question 14

transcranial magnetic stimulation (TMS)

Answer 14

• In TMS, a coil carrying an electrical current is held over the scalp, and a brief, focal magnetic pulse is generated which activates a small region of cortex (approximately 10 – 15 mm, depending on the size of the coil) underlying the coil. The activation acts like a ‘virtual lesion’,
• If a particular brain region is critically involved in a task, then TMS of that region should affect performance.

Question 15

Limitations of clinical neuropsychology

Answer 15

Patients often difficult to test intensively
Problem of replicability in single cases
Assumes local lesions have local effects
No control of lesion size or location in the brain – ‘experiments of nature’

Question 16

neuron

Answer 16

Neurons come in many different shapes and sizes. Almost all have four basic structures or regions:

Cell body– contains the nucleus (genetic material) and internal organelles necessary for cell maintenance.

Dendrites – the tree-like branches that allow neurons to communicate with one another. Dendrites receive information from other neurons.

Axon – a long, slender fibre that carries signals from the cell body. The signal carried by an axon is an action potential,

Question 17

Glial cells

Answer 17

• provide physical support
• assist with chemical transport to and from neurons
• provide insulation
• destroy and remove neurons that have died from injury or old age

Question 18

Resting membrane potential

Answer 18

the inside of an axon is more negatively charged than the outside. This difference, known as the resting membrane potential, is about -70 millivolts (mV, a thousandth of a volt).

Question 19

Depolarisation

Answer 19

-A very rapid reversal (depolarisation) of the membrane potential of an axon is called an action potential. The action potential constitutes the basic message that is transmitted down an axon from the cell body to the terminal buttons.

Question 20

The action potential (AP) – ion exchange across the axon

Answer 20

Normally the cell membrane is not very permeable to sodium Na+. But if the membrane were suddenly to became permeable to sodium Na+, sodium Na+ ions tend to rush into the cell, causing a sudden increase in the concentration of positively charged ions and changing the membrane potential. This change in membrane permeability is precisely what causes an action potential.

Certain protein molecules in the cell membrane, known as ion channels, provide an opening through which ions can rapidly enter or leave the cell. When ion channels for sodium Na+ open, sodium Na+ ions rush into the cell. Shortly thereafter, ion channels specific to potassium K+ open, allowing potassium K+ ions to rush out of the cell.

Question 21

AP

Answer 21

An action potential can be described as the following sequence of events:

1) Once a neuron’s threshold for excitation is reached, sodium channels in the cell membrane open and there is a rapid influx of positively charged sodium Na+ ions. This produces a sudden change in the membrane potential, from –70 mV to +40 mV (depolarisation).
2) Shortly afterwards (less 1 millisecond), the potassium channels also open, allowing positively charged potassium ions to leave the axon (repolarisation).
3) At the peak of the action potential (about 1 millisecond) the sodium channels close and cannot re-open until the membrane reaches its resting potential again (refractory period).
4) As potassium ions are moved out of the axon, the membrane slightly overshoots its resting value (hyperpolarisation) before returning to its resting level (–70 mV ).

Question 22

Saltatory conduction of the AP

Answer 22

Rather than moving as a single continuous wave down the axon, action potentials ‘jump’ into the gaps (Nodes of Ranvier) between segments of myelin that are wrapped around the axon (oligodendrocytes and Schwann cells).

Because an action potential is generated by the rapid influx of sodium Na+ ions into the cell, this process can only occur where the axon membrane is in direct contact with the extracellular fluid (i.e., at the Nodes of Ranvier). Within the myelinated portion of the axon, the electrical signal is conducted passively (like electricity down a wire) until it gets to the next Node, at which point another action potential is generated. Although the strength of the electrical potential decreases as it moves along myelinated portions of the axon, it is still large enough to trigger a new action potential at the next Node.

This jumping of the action potential along myelinated axons has two advantages. First, it saves energy because sodium-potassium transporters only have to work within the Nodes. Second, it increases the speed of neural signalling, and thus the speed with which we perceive, react and think.

Question 23

All-or-none law of the AP

Answer 23

Neurons have a threshold for excitation, above which an action potential will reliably be triggered. In other words, an action potential either occurs or it does not occur – the all-or-none law.

Once triggered an action potential remains at the same amplitude (i.e., its membrane reaches the same level of depolarisation), and travels down the axon to its end.

Question 24

Rate law of the AP

Answer 24

Variable information is signalled by the number of action potentials produced by a neuron (i.e., the neuron’s rate of firing). A strong muscle contraction is caused by a high rate of firing of a motor neuron; similarly, a loud sound is represented by a high rate of firing of an auditory nerve fibre.

Thus, the basic unit of information carried by axons is their rate of firing (known as the rate law).

Question 25

Multiple sclerosis

Answer 25

Begins with visual problems, numbness, weakness of the limbs
Ultimately leads to paraplegia, slurred speech, problems with vision and eye movements
Frequent ‘attacks’ followed by quiescence or remission
Autoimmune disorder that affects the insulation covering nerve cells (myelin)

Question 26

Structure of a synapse

Answer 26

Presynaptic membrane – the membrane of the presynaptic terminal button
Postsynaptic membrane – the membrane of the postsynaptic neuron
Dendritic spine – a ridge on the dendrite of a postsynaptic neuron, with which a terminal button from a presynaptic neuron forms a synapse
Synaptic cleft – the tiny gap between the presynaptic and postsynaptic membrane (approximately 20 nanometres wide; a nanometre is a billionth of a metre)
Synaptic vesicles – tiny balloons filled with neurotransmitter molecules; found in the release zone of the terminal button
Microtubules – long tubes that run down the axon and guide the transport of synaptic vesicles from the soma to the axon terminal
Release zone – part of the interior of the presynaptic membrane to which synaptic vesicles fuse in order to release their neurotransmitter into the synaptic cleft

Question 27

An action potential causes the release of neurotransmitter

Answer 27

Vesicles contain neurotransmitter (NT) molecules
An action potential in the presynaptic cell triggers vesicles to move toward the cell membrane
This is followed by a fusion of the two membranes
Neurotransmitter molecules are then released into the synaptic cleft
Ionotropic receptors have their own binding sites
When a neurotransmitter molecule attaches to a binding site, an ion channel opens (like a key in a lock)

Question 28

Neural integration - excitatory postsynaptic potential (EPSP)

Answer 28

Excitatory postsynaptic potentials (EPSPs) depolarise the postsynaptic cell membrane
EPSPs increase the likelihood that an action potential will be triggered in the postsynaptic neuron

Question 29

Neural integration - inhibitory postsynaptic potential (IPSP)

Answer 29

Inhibitory postsynaptic potentials (IPSPs) hyperpolarise the postsynaptic cell membrane
IPSPs decrease the likelihood that an action potential will be triggered
The combined effect of EPSPs and IPSPs is called neural integration

Question 30

Effects of drugs on synaptic functions

Answer 30

Drugs act upon the CNS in many different ways
Most drugs that affect behaviour do so by acting on synapses
Drugs that affect synaptic transmission are divided into two categories:
Agonists - facilitate activity of postsynaptic neurons
Antagonists – inhibit activity of postsynaptic neurons

Question 31

Navigating neural space

Answer 31

Rostral (anterior) – ‘toward the beak’
Caudal (posterior) – ‘toward the tail’
Dorsal (superior) – ‘toward the back’
Ventral (inferior) – ‘toward the belly’
The human neuraxis bends because the head is perpendicular to the back
Lateral-toward the side
Medial-toward the midline
Ipsilateral – structures on the same side of the body (in Latin ipse means ‘same’)
Contralateral - structures on the opposite side of the body (in Latin contra means ‘against’)

Question 32

Major divisions of the nervous system

Answer 32

The nervous system has two major divisions:
Central nervous system (CNS; includes the brain and spinal cord)
Peripheral nervous system (PNS; includes the cranial nerves, spinal nerves and peripheral ganglia)

The PNS is further divided into subcomponents:
The somatic system connects the CNS to voluntary muscles, whereas the autonomic nervous system connects the CNS to non-voluntary muscles and glands.

The autonomic nervous system is also subdivided into two systems that tend to operate in opposition:
 Sympathetic system (arousing; prepares the body for activity and therefore expends energy)
 Parasympathetic system (calming; prepares the body for restoration of energy)

Question 33

The meninges

Answer 33

The entire nervous system (CNS and PNS) is covered by a protective sheath of connective tissue.
The protective sheaths around the brain and spinal cord are called the meninges (plural). In the CNS there are three layers:
1) Dura mater (‘tough mother’) - the thick outer layer
2) Arachnoid mater (‘spider-like mother’) – the middle layer, which has a weblike appearance due to the protrusions called arachnoid trabeculae, and is soft and spongy.
3) Pia mater (‘pious mother’) – delicate inner layer, which follows every fold of brain tissue.

Question 34

Cerebrospinal fluid (CSF)

Answer 34

CSF: clear fluid, like blood plasma
reduces shock from head movements
Created by choroid plexus
reabsorbed into bloodstream

Question 35

Lobes of the cerebral cortex

Answer 35

Frontal lobe – includes all the cortex anterior to the central sulcus. This region is especially large in humans, relative other animals, and is responsible for our unique ability to plan, to reason, and to reflect on our own behaviours. [Recall the effects of frontal leucotomy in psychiatric patients.]
Parietal lobe – includes cortex located behind the central sulcus, caudal to the frontal lobe and dorsal to the temporal lobe. In the left hemisphere this region plays a special role in aspects of language comprehension and mental arithmetic; in the right it is involved in representing the locations of salient objects in space.
Temporal lobe – includes cortex located ventral to the frontal and parietal lobes. In the left hemisphere this region plays a role in understanding the spoken and written word; in the right it may be particularly involved in recognising complex objects and faces.
Occipital lobe – includes the cortex at the back of the brain, caudal to the parietal and temporal lobes. Cortex in this area processes various aspects of visual information, such as motion, colour, shape and so on.

Question 36

Difference in the left and right hemisphere

Answer 36

the left hemisphere controls many aspects of language, including talking, comprehension of speech, reading and writing. One way to think about the left hemisphere is that it seems to involve piecemeal, analytic processing; breaking down incoming sensory information to make sense of it.

In contrast, damage to the right hemisphere can cause problems with constructing objects or drawings from pieces (e.g., completing a jigsaw puzzle). One way to think about the right hemisphere is that it seems to be specialised for the synthesis of information; forming whole representations from separate pieces of incoming information.

Question 37

The forebrain

Answer 37

-The forebrain has two subdivisions, the telencephalon and the diencephalon.
The telencephalon is composed of the two cerebral hemispheres, which together form the cerebrum. The hemispheres comprise an outer layer called the cortex (‘bark’), and an inner (subcortical) region that contains the basal ganglia and limbic system.

-In humans, the cerebral cortex is highly convoluted (folded). It is characterised by large, deep grooves called fissures, smaller grooves called sulci (singular: sulcus), and bulging regions of tissue between the folds called gyri (singular: gyrus). The convolutions of the cerebral cortex allow a large amount of tissue to fit into a relatively small space (the cranial cavity).
-The cortex consists predominantly of the cell bodies and associated dendrites of neurons, together with the supporting glial cells. This region, which is around 3 mm thick, is sometimes called the grey matter, because of its greyish-brown appearance.

-Beneath the cortex run the axons of the neurons of the cortex, which connect these cells to those located elsewhere in the brain. The axons are covered in myelin (the white, fatty cells that insulate neurons), and so this region is often known as the white matter.

Question 38

Higher order function of the frontal lobes

Answer 38

Human frontal cortex is different from other animals
relatively larger than non primates
a higher level of connectivity with the rest of the brain (compared to other apes)
Functions of the frontal lobes
Voluntary, controlled behaviour
Language
Abstract reasoning & planning
Impulse control & emotional regulation
Social cognition

Question 39

The corpus callosum

Answer 39

Although the two cerebral hemispheres perform different functions, our perception, memory and thinking processes are unified. This is made possible because of a large bundle of axons that connects cortical areas of the two cerebral hemispheres, known as the corpus callosum. The corpus callosum contains about 200 million axons.

Some axons of the corpus callosum connect corresponding regions of cortex in the two hemispheres (homotopic fibres). Others connect different cortical regions of the two hemispheres (heterotopic fibres). Still others connect adjacent regions within the same hemisphere (ipsilateral fibres).

Patients with intractable epilepsy may have their corpus callosum surgically cut (callosotomy) to prevent abnormal electrical activity spreading from one hemisphere to the other. In such cases the two hemispheres essentially operate in isolation, with interesting consequences for behaviour.

Question 40

Limbic system

Answer 40

Buried inside the medial portion of each hemisphere resides a set of structures known collectively as the limbic system whose primary functions are motivation and emotion.
The most important parts of the limbic system are the hippocampus (‘seahorse’) and the amygdala (‘almond’), which are located adjacent to the lateral ventricle of each temporal lobe. A bundle of axons called the fornix connects these structures with other regions of the brain, most notably the mammillary bodies, two little nodules at the base of the brain that form part of the hypothalamus (described in detail later). A region of the cerebral cortex that lies above the corpus callosum, known as the cingulate cortex, is also considered part of the limbic system. This part of the limbic system controls many functions, one of which is the emotional response to pain.

Question 41

Basal ganglia

Answer 41

The basal ganglia (the word ganglion means ‘a swelling’) are a collection of nuclei buried deep within each hemisphere. They contain the cell bodies of collections of neurons, and thus are classified as grey matter even though they are not part of the cerebral cortex. The principal nuclei comprising the basal ganglia are the caudate nucleus (‘nucleus with a tail’), the putamen (‘shell’) and the globus pallidus (‘pale globe’).
Together, the nuclei of the basal ganglia are responsible for controlling movement, particular those aspects that are highly automatised or involuntary (such as walking).

Question 42

thalamus & hypothalamus

Answer 42

Thalamus:
Major relay station for sensory inputs to cerebral cortex
Divided into several nuclei
Hypothalamus:
Controls autonomic nervous system and endocrine system
Regulates survival behaviours (fighting, feeding, fleeing, mating)

Question 43

Midbrain

Answer 43

• The midbrain (mesencephalon) is located toward the base of the brain, and is anatomically the junction between the cerebrum and the spinal cord.
• The dorsal part of the midbrain is called the tectum (‘roof’). It consists of the superior and inferior colliculi (singular: colliculus). The brainstem is a generic term given to the set of structures that includes the diencephalon, the midbrain and the hindbrain, and is so named because of its (vague) resemblance to the stem of a plant.
• The inferior colliculi play a critical role in auditory processing, and in particular in our ability to localise sounds in the environment. The superior colliculi have a role in both auditory and visual processing, and may also have an important role in spatial localisation.
• The ventral part of the mesencephalon is the tegmentum (‘covering’), and it is located beneath the tectum. It contains several nuclei that have different functions.
• One cluster of nuclei in the tegmentum is known as the reticular formation, which is formed from a complex network of dendrites and axons (reticulum means ‘little net’). The reticular formation, which is widely connected with various parts of the brain and spinal cord, plays a vital role in sleep, arousal (i.e., the ability to remain conscious and alert), and various reflexes. Damage to this part of the brainstem can cause coma or death.

Another nucleus within the tegmentum is called the substantia nigra (‘black substance’). The nucleus gets its name from the black appearance of the cell bodies within it. These neurons produce dopamine, an important neurotransmitter. In Parkinson’s disease, a movement disorder, neurons in the substantia nigra degenerate and so are no longer able to convey dopamine to the motor nuclei of the basal ganglia

Question 44

Hindbrain

Answer 44

The hindbrain has two major divisions, the metencephalon and the myelencephalon.

The metencephalon consists of the pons and the cerebellum.

The pons lies on the ventral surface of the brainstem. It contains several nuclei important in regulating sleep and arousal; it also relays information from the cerebral cortex to the cerebellum, via the cerebellar peduncles.

The myelencephalon is more commonly called the Medulla
The Medulla links the hindbrian to the spinal cord, and contains neurons important for autonomic functions like respiration and hear rate.

Question 45

Cerebellum

Answer 45

It plays a role in the coordination of movement, and damage to the cerebellum causes problems with walking, standing and other aspects of motor (movement) control. The cerebellum receives information from the visual, auditory, somatosensory and vestibular (balance) systems, and from areas involved in the control of muscles

Question 46

Spinal column

Answer 46

Vertebrae:
Cervical (neck)
Thoracic (chest)
Lumbar (lower back)
Sacral (pelvic region)

Spinal foramen – hollow channel in which spinal cord resides

Question 47

Spinal cord

Answer 47

Grey matter surrounded by white matter
Surrounded by 3 meninges
31 pairs of spinal nerves (to receive and convey information)

Question 48

Dorsal and ventral root ganglia

Answer 48

The cell bodies of neurons that receive sensory information are located outside the CNS; axons from these receptor neurons (called afferent neurons, because they ‘bear toward’ the CNS) are found in the dorsal roots, and the cell bodies that give rise to them reside in the dorsal root ganglia (the swelling being due to the cluster of cell bodies).

The cell bodies of neurons that convey information from the brain to the glands and muscles are located inside the grey matter of the spinal cord; axons from these neurons (called efferent neurons, because they ‘bear away from’ the CNS) are found in the ventral root.

Question 49

Structure of the outer, middle and inner ear

Answer 49

The human ear consists of three basic parts:

• Outer ear: consists of the outer fleshy pinna, the auditory canal, and the tympanic membrane (eardrum). The tympanic membrane vibrates with the soundwaves that enter the auditory canal, and this signal is transmitted on to the middle ear.
• Middle ear: consists of three tiny bones called ossicles. The malleus (hammer) is connected to the tympanic membrane. It transmits vibrations via the incus (anvil) to the stapes (stirrup), which is connected to a structure called the cochlea (snail), which is part of the inner ear.
• Inner ear: consists of the cochlea, which contains the receptors for analysing sounds. The cochlea is a bony structure, but it has two small membranes that form windows on its fluid-filled interior. The stapes is connected to the oval window. Sound waves that cause the stapes to move in and out move the fluid over receptors inside the cochlea. Because the cochlea is a closed structure, another membrane is needed to allow the fluid to move: this membrane is called the round window.

Question 50

The cochlea

Answer 50

contains the basilar membrane runs along the length of the cochlear
The cochlea converts mechanical movement of the ossicles into fluid movement along the basilar membrane
Movement of stirrup against the oval window
The round window deforms to allow the movement

Question 51

Organ of Corti

Answer 51

runs all the way along the length of the cochlea. The Organ of Corti is composed of the basilar membrane at its base, receptors in the middle called hair cells (inner and outer), and a rigid shelf over the top called the tectorial membrane

Question 52

Spiral ganglion cells & the auditory nerve

Answer 52

• When the stereocilia are moved ion channels are opened which in turn cause receptor potentials in the hair cells. The hair cells secrete a neurotransmitter that triggers action potentials in neurons called spiral ganglion cells. The axons of many thousands of spiral ganglion cells are grouped together to form the auditory nerve
• The axons of auditory nerve neurons form synapses with neurons in the medulla (part of the brainstem), which in turn send their axons to other parts of the brain for further processing

Question 53

Place coding of frequency along the basilar membrane

Answer 53

Sounds of different frequencies cause different regions of the basilar membrane to flex back and forth. Specifically, higher frequencies produce greater displacements of the basilar membrane toward its basal end, and lower frequencies produce more displacement at its apex
Different frequencies of sound are therefore coded by the particular spiral ganglion cells that are active along the basilar membrane, and this information is transmitted via the auditory nerve to the brainstem and other parts of the brain

Question 54

Tonotopic organisation of primary auditory cortex

Answer 54

The primary auditory cortex is located in a region of the temporal lobe called the superior temporal gyrus . Much of this cortical region is buried inside the deep fold of the lateral fissure, and is therefore not visible from a lateral view of the brain.

Just as the basilar membrane represents different frequencies along its length, so the primary auditory cortex is organised as a tonotopic map, with lower frequencies represented more anteriorly and higher frequencies more posteriorly.

Question 55

Cochlear implants

Answer 55

Bypass a dysfunctional hair cell stage
Electrically stimulate spiral ganglion cells
Implant an electrode array along the cochlear
Process sound and break it up into different frequencies
Match the voltage to the electrode location to induce action potentials in spiral ganglion cells that mimic the sound
Voice recognition requires relatively few electrodes
Music appreciation requires many more electrodes to cover the broader frequency range of music compared to speech

Question 56

The human eye

Answer 56

The eye contains the peripheral apparatus necessary for transducing (transferring) light into a neural signal.

Light enters the eye through the transparent outer layer known as the cornea. Immediately behind the cornea is the lens, which is made up of a number of transparent layers, much like an onion. The shape of the lens can be altered to help focus the image onto the back of the eye, which is lined by a light sensitive structure called the retina. The eyeball itself is filled with a clear gelatinous fluid called the vitreous humour.

Note that the light sensitive cells in the retina (the rods and cones) send their axons out of the eye from a common point, known as the optic disk. Because there are no photoreceptors at the optic disk, it causes a blindspot (i.e., the region of space from which an object is not visible). The axons that are bundled together at the optic disk are known collectively as the optic nerve.

Question 57

Cone response to light from an object

Answer 57

To appreciate how neurons in the brain encode visual information from the eye, it is necessary to understand how the photoreceptors, bipolar cells and ganglion cells interact in the retina.

There is a convergence of information from the photoreceptors, through the bipolar cells to the ganglion cells. The responses of many photoreceptors are combined to influence the response of a single ganglion cell.

Each ganglion cell responds to signals from one small cluster of photoreceptors, which in turn are excited by light from one small region of the visual field (this is known as the cell’s receptive field). The photoreceptors exert an excitatory influence on the bipolar cells with which they form connections. Adjacent bipolar cells can then have either an excitatory or inhibitory influence on a single ganglion cell.

Receptive fields of ganglion cells tend to have a centre-surround organisation (like a two-dimensional doughnut). ON cells are excited by light in the centre of their receptive field, and inhibited by light in their surrounding field. In contrast, OFF cells are inhibited by light in the centre of their receptive field, and excited by light in their surrounding field. These two simple types of receptive field provide a powerful mechanism for signalling edges and borders in the visual world, which in turn forms the basis for higher level visual recognition.

Question 58

Modular organisation of specialised visual areas

Answer 58

The primary visual cortex is divided into several functional modules or subregions, each of which contains neurons that have specialised properties for extracting specific information from the visual input.

• The primary visual cortex (also known as visual area 1, or V1) is the first cortical region to receive axons from visual cells in the lateral geniculate nucleus. Area V1 in each hemisphere contains a retinotopic map of the contralateral half of the visual field.
• Patients with damage that involves an area of visual cortex called V4 are no longer able to perceive colour in the contralateral visual field
• lost of ability to perceive visual motion after the damage of area MT bilaterally
• lesions elsewhere in the visual association cortex can impair the ability to recognise familiar objects, but leave motion and colour vision intact.Selective loss of the ability to recognise familiar objects through the modality of vision is called visual object agnosia

Question 59

Face regconition

Answer 59

It has been suggested that the brain has specialised visual areas devoted to processing the subtle differences in configuration of the eyes, eyebrows, mouth, nose, chin and so on – all the features that go together to make a particular face unique

Question 60

Face blindness (prosopagnosia)

Answer 60

Several studies have suggested that a region of the inferior part of the temporal lobe called the fusiform gyrus is particularly important for face recognition.

Human patients with damage of the fusiform gyrus, either bilaterally or in the right hemisphere alone, may have a selective impairment in recognising familiar faces, even though their ability to recognise other objects may still be relatively good. A problem in recognising familiar faces is called prosopagnosia.

Question 61

Cells of the retina

Answer 61

The retina can be divided into three distinct layers:
Photoreceptor layer
Bipolar cell layer
Ganglion cell layer
The rods and cones form synapses with bipolar cells, which in turn form synapses with ganglion cells. Ganglion cells send their axons through the optic nerve (the second cranial nerve), which conveys visual information to the brain. Two other cell types in the middle layer of the retina, horizontal cells and amacrine cells, serve the function of combining messages from several photoreceptors.

Question 62

The concept of emotion

Answer 62

Emotions consist of patterns of physiological response and species-typical behaviours.
In humans these physiological responses are accompanied by feelings.
Feelings are powerful motivators
Emotions are likely to have evolutionary significance (Charles Darwin;1872)
emotional expressions convey an animal’s intentions
Three-component of emotion Behavioural
Autonomic
Hormonal
Behavioral

Question 63

Neural control of emotional response patterns

Answer 63

Bard (1929)
Observed ‘sham rage’ in cats whose cerebral hemispheres had been surgically removed
Sham rage absent after removal of hypothalamus

Question 64

Klüver-Bucy syndrome and the amygdala

Answer 64

Klüver and Bucy (1939)
Bilateral ablation of temporal lobes in rhesus monkeys
Impaired visual recognition (‘psychic blindness’)
Oral exploration of objects; hyperphagia
Impulsive and stereotyped actions; aberrant sexual behaviour
Absence of fear

Question 65

Structure of the amygdala

Answer 65

The amygdala (or more accurately, the amygdaloid complex) is located in the anterior temporal lobe, and consists of several nuclei with different functions

-Lateral nucleus: receiver input from sensory cortex and sensory thalamus and relay it thourgh different nucleus to the central nucleus
-Central nucleus output to hypothalamus causing physiological change
-lesion of the central nucleus lead to the abolish of fear
-stimulations to the central nucleus is enough to induce fear and agitation
-

Question 66

James-Langs theory

Answer 66

William James (1842-1910) and Carl Lange (1834-1900) independently suggested similar explanations for the feelings associated with emotions. According to the James-Lange theory, an emotion-inducing stimulus or event triggers an appropriate set of physiological responses (controlled by the autonomic nervous system), such as increased heart rate and breathing, sweating, etc., as well as particular behaviours, such as clenching of the fists and teeth. The brain receives feedback from sensory receptors in the skin, muscle and internal organs that produce these responses, and this feedback generates the subjective feeling of emotion. In other words, according to the James-Lange theory our emotional feelings are determined by the way in which we interpret the sensory feedback we receive from our physiological response to an emotion-inducing stimulus. This is opposite to the view many people have, which is that emotional feelings are experienced directly.

Question 67

Cannon-Bard theory

Answer 67

In 1927, the physiologist Walter Cannon criticised James Langs theory, saying that the internal organs provide only very diffuse and slow sensory feedback which could not account for the salience and immediacy of emotional feelings. He proposed instead that emotion-inducing stimuli have two independent effects: they excite a feeling of emotion and also a range of physiological effects controlled by the somatic and autonomic nervous systems. The theory was expanded and promoted by Bard, and has come to be known as the Cannon-Bard theory.

Question 68

The orbitofrontal cortex and the somatic marker hypothesis

Answer 68

– frontal lobes associated with physiological traces that guide social & emotional decision making

• Decision making guided by emotional evaluation of the consequences of our actions
• Faced with the same decision activates memories of past events
• These representations activate traces of the bodily reaction to previous behaviour
• Feelings steer us towards decisions that decrease negative feelings and increase positive feelings
• Allows us to anticipate the emotional consequences of our actions

Question 69

Schachter & Singer’s two-factor theory of emotion

Answer 69

Schachter & Singer’s two-factor theory of emotion

• physical arousal plays a primary role in emotions but arousalis the same for a wide variety of emotions
• We must identify the arousal in order to feel the emotion
• Depends on context & memories of previous experience
• Feelings are an interaction between physical arousal and the cognitive label given to that arousal

Question 70

Amygdala pathways and fear conditioning

Answer 70

-Joseph Le Doux suggested that there are two pathways subserving fear conditioning in the human brain
1) ‘Low road’ – quick but dirty
(thalamus  amygdala)
2) ‘High road’ – slow but detailed
(thalamus  sensory cortex  amygdala)
-The low road is thought to ready or prime the amygdala quickly, so that it is ready to respond to the more detailed information from the high road if this corresponds to the conditioned stimulus. This two-pathway mechanism allows for both fast and accurate responses to potentially threatening events.

Question 71

Visual pathways & field defects

Answer 71

Damage to the primary visual cortex (area V1) causes blindness in the region of the visual field represented by the affected area of cortex. Thus, a small unilateral lesion of V1 will lead to a scotoma (i.e., a small patch of blindness) in one hemifield; unilateral destruction of V1 in its entirety will cause blindness in the whole of the contralateral visual field (an homonymous hemianopia); and total destruction of V1 bilaterally will result in complete cortical blindness (i.e., an absence of conscious vision in both visual fields). Early experiments in monkeys with extensive or complete removal of area V1 bilaterally showed that the animals could nevertheless respond in simple ways to visual stimuli, by making hand or eye movements to visual targets, or by detecting and discriminating between different visual stimuli at above-chance levels. In other words, even though the monkeys were rendered ‘blind’ by cortical ablation of the primary visual cortex, they could still use vision to perform certain tasks.

Question 72

Blindsight - a disorder of conscious vision

Answer 72

Occurs following unilateral damage restricted to the primary visual cortex
Above-chance visual performance in the‘blind hemifield
Patient may show preservation of:
pupillary reflexes
manual and saccadic localisation
wavelength & motion discrimination
orientation & shape discrimination
Neuropsychological studies by Weiskrantz
Sanders, Warrington, Marshall, & Weiskrantz (1974)
Also used ablation in non-human primates

Question 73

How does visual information get to the brain in blindsight?

Answer 73

Recall that beyond the optic chiasm, axons in the optic tracts continue posteriorly until they form synapses with neurons in a part of the thalamus called the lateral geniculate nucleus (LGN; there is one in each hemisphere). Neurons in the LGN send their axons posteriorly where they form synapses with neurons in the primary visual cortex. Note that about 90% of retinal axons course through the LGN on their way to the primary visual cortex, forming the so-called geniculostriate pathway. After damage to the primary visual cortex, these inputs are rendered ineffective, resulting in blindness.

But a further 10% of retinal axons bypass the LGN altogether, and project instead to the superior colliculus (SC; part of the midbrain) and pulvinar nucleus of the thalamus, which in turn send axons on to other visual areas of the cortex. You will recall that the SC is involved in controlling the orienting response to sudden visual and auditory stimuli. It seems likely that activity in the SC, pulvinar, and the cortical regions to which they project, underlies the remarkable preservation of some visual capacities in blindsight patients. But note that without direct input from the LGN to primary visual cortex, there is no longer any conscious visual experience. Thus blindsight provides a striking example of a neuropsychological dissociation between conscious and unconscious perception.

Question 74

Damage to the parietal lobe causes unilateral spatial neglect

Answer 74

Occurs after damage to one side of the brain (usually the right hemisphere)
Patients behave as if the affected side of space (the contralesional side) has ceased to exist:
ignore food on one side of their plate
fail to shave or make-up one side of their face
bump into objects on one side
fail to read text from one side of the page
Most common and severe after damage to the parietal lobe

Question 75

Unconscious perception inspatial neglect=

Answer 75

despite the absence of conscious perception in neglect, such patients may nevertheless process some aspects of the neglected stimulus unconsciously. Such unconscious perception is likely to be subserved by neural pathways that extend from the primary visual cortex (which remains intact in most neglect patients) into the object recognition pathways of the temporal lobe. Damage to the parietal cortex impairs selective attention, and so patients remain unaware of perceptual inputs on their affected side; but the object recognition pathways continue to function normally, processing object identity without the patient’s explicit knowledge.

Question 76

Covert selective attention reveals prioritising by the brain

Answer 76

Helmholtz made a large screen in which letters were positioned at various distances from the centre. He then hung the screen on a wall of his laboratory, and excluded all light so that the entire lab was in complete darkness. Helmholtz then used a machine to create an electrical spark, which briefly illuminated the screen, much like a camera flash. Although there were far too many letters to see at any given moment in time, Helmholtz found that by keeping his eyes fixed on the centre of the screen he could pay attention to a selected region in advance (in other words, he attended covertly to a part of the screen, without actually moving his eyes to foveate it). He found that he was able to discriminate all the letters within the attended region, but was unable to do so for the rest of the letters on the screen.

By this simple experiment Helmholtz had demonstrated an important principle, namely, that voluntary allocation of attention can enhance perception of stimuli in a selected region of space, despite the receptors (in this case the retina) remaining fixed.