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What is consciousness? How is is produced by the brain?

Consciousness represents the highest level of brain functioning. There is no single area that can be attributed to function of consciousness. The most popular theory about consciousness is the Baar's theorem. Bernard Baar suggested in 1938 that the sensory systems are processed in the cortex, yet still does not reach conscious level. However, if all this information is broadcasted to a certain parts brain, which make up the global workspace, consciousness is achieved. These global workspace areas are thought to be the prefrontal cortex, cingulate gyrus, and the parietotemporal association cortex.

1

What happens when the two cerebral hemispheres are surgically separated?

Functions lateralised to only side of the hemispher cannot work with the information processed by the opposite side of the cerebrum. In these cases the brain makes separate responses based on the different information processed in each cerebrum. Therefore, both sides experience different states of consciousness.

2

How long does the sensory information take to reach consciousness level?

300 millisecond after the cortex receives an important sensory information. This was discovered by the French team led by Dehaene and Changeux.

3

Why is memory important for consciousness?

Memory is important for consciousness because it creates context for the situations of the present.

4

What is memory?

Memory is the ability to recall past events and use them as reference to take a better outcome in future events. There are three types of memory. They are episodic, the events that occurred in the person's life, semantic, the factual information and finally motor memory, which is the optimisations of common patterns of activity.

5

What did Eric Kandel discover?

Eric Kandel discovered the molecular changes during learning. He and his colleague discovered the simple biochemical changes that were associated with short term memory formation. The research was carried on the marine mollusc APLYSIA. He won the Nobel prize in 2000 for this.

6

What are the basic mechanisms of learning?

1. Change of neurotransmitter usage in neurons
2.The amount or rate of neurotransmitter released, or the number and type of receptors in the post synaptic cell.
3. Large scale alterations of the the brain by the disassembling, regrowing or physically altering the dendrites and possibly even their axons.
4. In some parts of the brain, even the addition of new neurons to replace the old neurons.

7

What is the Hebbian learning?

Hebbian learning was a psychology theory that was suggested by Hebbian in the 1940. He said that "neurons which fire together, wire together". This is an important stepping stone to the modern theories of molecular mechanisms of learning and memory.

8

Elaborate on the changes of neurotransmitters during learning.

During learning, one observed molecular change is the change of neurotransmitter to have a different effect on the postsynaptic cell. This commonly happens during development when some neurons start out by using glutamate(excitatory), then shift to GABA(inhibitory) and finally glycine(inhibitory) when the connections are worked out. This method is commonly seen in early development of the brain and less in the mature brains. After development, the neurotransmitters used are fairly stable

9

Elaborate on the the effect on increased amount or rate of neurotransmitter released, or change in number and type of receptors.

These changes can greatly alter the side and quality of the influence transmitted, and an occur very rapidly as receptors and vesicles are shifted to and from membranes. This phenomena is the most commonly studied mechanisms of learning commonly known as long term potentiation, long term depression and spike timing dependent plasticity.

10

How does LTP, LTD and spike timing dependent plasticity achieved?

Through balanced biochemical interactions between enzymes, transport proteins and release of calcium ions allows patterned activity to be long lastingly strengthened or make make long lasting changes on the type of synaptic connection.

11

Elaborate on the functioning of changes in dendrite and axon shape on learning.

Silencing of many synaptic inputs can lead the dendrites to retract and find active inputs. This type of large scale reorganisation is termed plasticity to salvage the functions of the brain which have been lost due to injuries.

12

Why is neurogenesis important in learning?

Neurogenesis in the hippocampus is particularly important as neurons tend to exhaust functional capacity to learn and these neurons are replaced with new ones through neurogenesis.

13

What is needed to be known by the nervous system to properly execute behavioural plans of movement of the brain?

The nervous system has to know the relationship between each muscle and body part to execute behavioural plans of movement properly.

14

Why is motor learning important?

Motor learning is important because the optimisation and automation of movement is important as genetics can result the muscle and bones to grow differently in each person. The body has to learn to move effectively after the adverse effects of arthritis, fatigue, injuries, exercise, infections and the circulation of hormones can have in the muscle strength.

15

What are some of the most common relationship between muscles observed?

The inhibition of the antagonist muscle while exciting the protagonist muscle, which is achieved by an inhibitory interneurons. The different reflexes to compensate for postural shifts,and imbalances are also some relationships the body has built.

16

How is motor learning useful in actions such as throwing a ball?

The brain, especially the cerebellum and the secondary motor cortex, works together to organise the movements to complete a goal. The first time the sequence is activated, the body follows the sequence action after action. This looks clumsy and is ineffective. However, during repetition, the cerebellum corrects the sequence each time so the body executes it in proper timing. This makes the movement more fluent and effective. After the action is mastered, it is automated by the body to form a module. This allows the brain to concentrate on more important details such as where to throw the ball and white how much force.

17

What is the hippocampus?

The hippocampus is a three layered cortex in the temporal lobe that is important in the formation of episodic memory. It is also found in non mammalian animals but is not as impressive. It is still effective, especially in birds where it can help them to remember 30000 hiding spots of food. Their hippocampus apparently enlarges by 30% during hoarding season. In most small mammals, the hippocampus takes up 10% of the brain but in humans it is overshadowed by the association areas of the frontal and temporal lobe.

18

Give an example of gap in experience ?

A clinical procedure by which the drug midazolam can be used to boost GABA receptor activity in the hippocampus to prevent the formation of episodic memory of recent events. This is due to the active suppression of the hippocampus. People can cooperate throughout the procedure but retain no memory of it afterwards.

19

Why is hippocampus important for consciousness?

The hippocampus is not directly related to consciousness, however the episodic memories as it provide context to the surrounding and time in which the person is present in. Henry Molaison(HM) who underwent the bilateral removal of parts of his temporal lobe, including the hippocampus. He reported that waking up was always like waking up from a dream. Since he did not have context for time, he was very disturbed in later decades when he saw he was ageing.

20

What are some of the major subdivisions of the hippocampus?

The subdivision of the hippocampus are dentate gyrus, cortical association areas, the subiculum and the entorhinal cortex.

21

What did O'Keefe and his colleague research on?

O'Keefe researched on cells that responded to spatial position, which were located in the hippocampus and the adjacent entorhinal cortex.

22

What is the effect of stress on the brain?

Too much stress can lead to the breakdown of the hippocampus function and the loss of memory at that point. This is why some traumatic events cannot be recalled by some people. Stress hormones does not allow the plasticity to occur in hippocampus.

In humans, the paraventricular nucleus of the hypothalamus controls the releases the control the release of cortisol from the adrenal gland. The amygdala promotes the release of cortisol, while hippocampus inhibits it. During stress, the functioning of the amygdala is stronger and persistence of stress can cause the hippocampus to lose control over the release of stress hormones. This causes a permanent reduce in the hippocampus ability.

23

How does the hippocampus structures work?

The entorhinal cortex helps to link events to places by registering incoming information on a 2D grid in the brain. This information is sent to the dentate gyrus, which sends mossy fibres to the CA3 region. The CA3 region projects to the CA1, which in turn sends the information to the subiculum. This is called the tri synaptic pathway.

The layer 2 sends information to the dentate gyrus and through the tri synaptic pathway, however this layer also directly projects to the CA3. All this information is passed onto CA1 through Schaffer collaterals. The layer three of the entorhinal cortex also projects to the CA1.

24

How is the effect on stress exhibited in rats?

The Morris water maze is a test used to test the hippocampal functions of the rats. The rat is placed in a pool of water that has an escape platform which is submerged in the water. The time taken to find the platform over the repeated tests should decrease for normal hippocampal functions. However, chronically stressed rats fail to remember the location of the platform compared to the non stressed rats.

25

What is the effect of severe stress in the brain?

The dendrite branches are lost during severe stress. Of the stress only persists over a short period of time, the damage is irreversible but prolonged stress can kill the hippocampal neurons. Victims of chronic sever trauma, often have reduced hippocampal volume in MR scans. They exhibit significant deficits in memory without any compromise to IQ or cognitive functions.

26

How does the emotional stimulus affect the brain?

It is sent to the sensory thalamus, which projects to the sensory cortex. The sensory cortex then sends this to the perhinal cortex, para hippocampal cortex and the entorhinal cortex, and the amygdala. The perhinal cortex, para hippocampal cortex and the the entorhinal cortex projects to the amygdala and the hippocampus. The amygdala stimulates the paraventricular nucleus, while the hippocampus inhibits it. The paraventricular nucleus depending on the influence stimulates or inhibits the pituitary gland to release ACTH. The ACTH stimulates the adrenal cortex to release cortisol, which affects the hippocampus and the amygdala.

27

What is the role of the cerebral cortex in episodic and semantic memory?

The hippocampus is crucial for memory. However, the memory is stored in a larger area of the cortex. The cortex also receives sensory input which shapes the cortical regions. The changing of connections due to the sensory inputs leads to semantic memory. Both of these memories are used together to predict the outcomes of planned actions and executes the action with least expected negative outcomes.

28

Which memory stays longer?

Semantic memory lastly longer while individual episodes are forgotten as we age.

29

Why is sleep said to be important?

Sleep is said to be important for the formation of memories.

30

How does sleep very between animals?

Other mammals can sleep from three hours to twenty hours day or with varying levels of alertness, such as sleeping half the cortex at a time.

31

What is a common myth of sleep?

We sleep to conserve energy, however energy is used during sleep. Maybe during deep sleep, we conserve energy but during REM sleep the body still uses energy.

32

How does a sleep cycle run for?

A sleep cycle runs for every 90 minutes. The proportion of slow wave activity in the ECG gradually becomes greater with each cycle until it reaches deep sleep. This cycle is followed by short periods called REM sleep, which is similar to being awake. REM sleep is when we dream.

33

Characteristics of REM sleep.

High levels of acetylcholine

34

What is the role of REM Sleep and deep sleep ?

REM Sleep is testing how cortical knowledge deals with recent events and deep sleep has an update of the cortex on the basis of the testing. During Slowwave sleep, acetylcholine levels are much lower permitting the hippocampus to consolidate the information into the structure of the cortex.

35

What are awake centers. Name them.

Awake centers are groups of neurons in the hind brain that keep the brain active. These are locus coeruleus, serotonin raphe system, the dorsal tegmental nuclei and the tubero mammilaary nucleus of the hypothalamus.

36

What is so special about the awake system ?

Each of the awake systems relies on a different NT. Locus coerules uses noradrenaline , serotonin in the raphe system , acetylcholine in dorsal tegmental nuclei and histamine in the tubero mammillary nucleus.

37

What happens when these systems shut down ?

Sleep occurs when the systems are shut down.

38

What was discovered by Falck and Hilarp ?

A method to identify noradrenaline dopamine and serotonin cell groups in the brain stem by making them fluoresce.

39

What did Von Economo discover ?

While working in vienna during the viral encephalitis epidemic of 1905, he was able to examine people who were died from 3 different types of sleep disorder. They suffered from
a.intense sleepiness - lesions in junction of hypothalamus and midbrain, damage to brain stem center or ascending pathways keeping the brain alert. Damage to awake centres
b. insomnia - lesions in anterior hypothalamus and pre-optic area suggesting damage to a center that makes the brain go sleep. Damage to VLPO
c. narcolepsy - lesions in posterior half of the hypothalamus and suggested a center to stabilize the relationship between sleep and wakefulness was located there. Damage to dorsal medial hypothalamus.

40

Where is the master sleep center and what is it called.

Ventrolateral-preoptic-nucleus is located in the rostral hypothalamus in the preoptic area

41

What is the function of VLPO

When the VLPO is activated it makes inhibitory connections with the awake centers and makes the brain go to sleep.

42

VLPO Damage

Pathological insomnia - Permanent inability to sleep

43

What is the suprachiasmatic nucleus ?

Suprachiasmatic nucleus is a biological clock that tells the VLPO when to sleep

44

What happens during narcolepsy

The dorsal medial nucleus of the hypothalams is damaged

45

Role of the dorsal medial nucleus of the hypothalamus

It has a stabilizing role, continually monitoring activity and behavior , and recognizing when danger or other factors make sleep inappropriate. This occurs even when VLPO says it is time to sleep.

46

What is special about histamine ?

Only the tubero mammillary nucleus of the hypothalamus uses histamine in the whole of the brain.

47

What are some biological clocks we have ?

The 24 hour clock which is regulated by the optic nerve. This is called circadian rhythm. Yet another biological clock times the release of hormones during ovulation. Pre-botzinger nucles is the respiratory rhythm pace maker. Cerebellar timing system is the inferior olive.

48

What controls ovulation ?

by the secretion of gonadotrophin releaseing hormones which causes the pituitary gland to release FSH and LH which cases ovary to secrete estrogen.

49

Where is amygdala located ?

Amygdala is a cluster of nucleus located in the temporal lobe of the cerebrum.

50

How can the amygdala be divided and what are their functions ?

Cortical or medial group is related to the olfactory system where as the lateral or the basal group is involved in complex circuits relating to emotional responses particularly fear.

51

What and how does the basal amygdala respond ?

Responds to sensations relating to danger and can react by stimulating the autonomic and endocrine centers through the hypothalamus.

52

What did Henrich Kluver and Paul Buci discover ?

They found removing the amygdala of rhesus monkeys had a significant effect on aggressive tendencies and response to fearful situations. This is called Kluver Buci Syndrome. The monkey also appeared to have good visual perception but poor visual recognition. They were reduction in aggression and fear.

53

What is the effect of stress on amygdala ?

It enhances amygdaloid functions in some traumatic event, the individual may have lost conscious memory but may retain very powerful unconscious emotional memory through amygdala mediated fear conditioning. These fears may become resistant to extinction and consequently an unconscious source of intense anxiety.

54

What is aggression ?

Exertion of dominance over other members of the same species. This was described by Konrad Lorenz who won the nobel prize in 1973.

55

What is pecking order ? Why is it important ?

Hierarchial behaviors that are due to the amygdala. Damage to amygdala can also cause lack of personal space.A higher position in hierarchy gives an animal preferential access to food and mates. It suggests hierarchy minimizes conflicts between members of group.

56

Why to avoid the term limbic system ?

Because every text book bags different parts of the brain together under this term. It is not consistent.

57

What is the potent region for reinforcing goal oriented behavior

The ventral tegmental area in the mid brain and adjacent regions.

58

How does the reward system work ?

The neurons of the VTA sends dopaminergic fibres to the nucleus accumbens of the forebrain.This bundle is called the medial forebrain bundle. The activation of the nucleus accumbens signals that something worthwhile has happened to the cortex. This causes neural activity in the ventral pallidum and the orbito frontal cortex which is associated with the feeling of pleasure.

59

How does drugs work ?

Drugs activate the medial forebrain bundle and produce the feeling of pleasure in the absence of goal oriented behavior.This is the basis of addiction.