Sleep Mechanisms, Cognition and Memory

Question 1

What happens to the cortex if its left to itself?

Answer 1

Reverts to slow waves (intrinsic property)

• So without other influences cortical cell activity becomes synchronised.
• Therefore if you remove the cortex from ascending inputs you would get S-wave sleep

Question 2

How is arousal controlled?

Answer 2

Arousal is under the control of a number of brain areas which stimulate the cortex into wakefulness.
A major area is the Ascending Reticular Activating System (ARAS) = part of the reticular formation in the midbrain.

ARAS recieves input from all the major sensory systems and makes connections with the whole of the brain and the spinal cord.

Stimulation of the ARAS -> Arousal from sleep

Question 3

How does the ARAS play into the awake state?

Answer 3

All the sensory inputs to the ARAS maintain a high level of activity in its neurones which is relayed to the rest of the brain as facilitory action.

ARAS neurones are also affected by circulating levels of norepinephrine and epinephrine which increase arousal

Question 4

At its simplest, how do changes in conciousness come about?

Answer 4

Changes in state of consciousness need changes in ARAS activity.
So in order to sleep need something to inhibit the ARAS

Question 5

Which areas of the brain are “sleep centres”?

Answer 5

There is still great uncertainty about this.
Neurones in the brainstem, hypothalamus and proptic area have all ben implicated. BUT the precise relationship and connections between them have not been elucidated.

Lesions in the lower brainstem at the midpontine level -> insomnia in animals

Question 6

What controls the sleep cycles?

Answer 6

Cycles of S->D and D->S sleep which occur through the night are due to oscillatory activity in 2 areas in the reticular formation.
-The Gigantocellularis Tegmental Field (GTF)

The GTF exhibits oscillatory activity, bursts of APs appear just before and during REM sleep.
GTF activity modifies cortical activity directly and through the ARAS. (S->D Sleep)

The Locus Coeruleus (releases NE), acts as an oscillator with the GTF.
When LC cells are active, GTF are not and vice versa.
Thus get D->S sleep

Question 7

What is the GTF?

Answer 7

The Gigantocellularis Tegmental Field (GTF) consists of very large cells with incredibly long axons and dendrites that make multiple connections throughot the brain.
A single GTF cell may contact a million other cells.

GTF is the origin of the PGO spikes which give the visial components to dreams.

GTF activity modifies cortical activity directly and through the ARAS.
Neurones are cholinergic (Cholinesterase inhibitors increase duration of REM sleep)

Question 8

Sleep is part of the circadian rhythmicity of biological systems.
What is circadian rhythmicity?

Answer 8

Basically biological systems show oscillations with an about 24 hour periodicity.
Localisation of the “master clock” is in the suprachiasmic nucleus (SCN) of the hypothalamus, lying just above the optic chisma.
Inhibition from the hypothalamus turns off orexin neurones at night.

Question 9

How in built is the circadian rhythm?

Answer 9

SCN neurones have an inherent approx 24 hour cycle, even after removal to an organ bath.
There are other “clocks” too, if you destroy the SCN there is still circadian rhythm of temperature.

Question 10

What cues control circadian rhythm?

Answer 10

These internal endogenous rhythms are ENTRAINED by external cues such as light/dark cycles.
Some of the nerve fibres on the optic nerve pass to the SCN.
Temperature and other cues also help to entrain rhythm so that blind people may also have circadian rhythms.

Question 11

What connections does the Suprachiasmatic Nucleus make?

Answer 11

Specific connections between the SCN and sleep areas have not been convincingly established.
But if the SCN is destroyed, then the circadian rhythm of sleep is lost.

Connections between SCN neurones and orexin secreting neurones, probably account for the circadian rhythm of sleep, stimulating wakefulness in the morning, when orexin level rises and sleep at night, when its level falls

Question 12

If people are kept in caves with no cues as to light or time how would this affect their sleep.
What does this mean for us in modern times?

Answer 12

People in caves will gradually increase their day length, initially 25 hours but may eventually become a 30 hour cycle.

This explains why jet lag is les bad travelling west than east.
Traveling west lengthens subjective day, easier to cope with than shortened day.

Question 13

How can frequent changes in time zones and work patterns affect health?

Answer 13

Frequent changes in time zones (as occur in flight crews) and frequent changes in work pattern (in shift workers) can lead to disruption of behaviours, particularly of sleep and attention deficits.

Long term health effects, 3x increase in CVS and GI disease after 10 years of shift work

Question 14

Give an introduction to Cognition and Memory

Answer 14

Cognition relates to the highest order of brain function and relates to behaviour that deals with thought processing.
However, it is really important to recognise that many of our behaviours are related to emotions.

It is the limbic system that acts as the link between our higher cognitive functions and the “more basic” emotional responses.

Question 15

How should you really think of the brain?

Answer 15

The brain is actually association areas, rather than specific function, so think of the brain as multiple parallel processing units.

Question 16

How can you show the importance of the frontal cortex in activities like planning?

Answer 16

PET scan shows a normal brain performing complex planning activity where the brain needs to create solutions to a problem.

Imaging shows the frontal lobe lights up with activity.
You may even be able to subtract the PET scan of the same brain idling to show the difference in frontal cortex lighting.

Question 17

How can we learn brain function from patients who suffer extreme damage to areas of the brain?

Answer 17

Vietnam veteran who suffered shrapnel wounds to his frontal lobes lost the ability to plan.
He’s gone from a bright promising, assertive soldier to an unemplyable person who makes multiple mistakes in his behaviour and his social relationships.
He now works as a hospital janitor.

The damage to his frontal cortex means he is no longer able to cope unless he is given very structured step-wise instructions.
He is no longer able to rely on internal thinking to develop an execute plans.
He has also lost reflective ability.

Question 18

What is the limbic system?

Answer 18

The limbic system is involved in emotion, learning and memory, very strong connections with temporal and frontal lobes.
So although it represents the “old” cortex, it has really important connections with the “neo”cortex.

Phyogenically the oldest part of the cortex, involved in olfaction. There is disagreement over which bits constitute the limbic system.

Together with the hypothalamus, responsible for instinctive and emotional behaviour (e.g. drives for thirst, sex, hunger etc) Used to do everything.

Question 19

How is the limbic system involved with reward and punishment?

Answer 19

Involved in reward and punushment aspects of behaviour.

Electrical stimulation of certain areas in the limbic system in consious patients -> intense feelings of well being, euphoria and sexual arousal = reward areas.
Reward centres have in common connections with ascending noradrenergic fibres and dopaminergic fibres in the mesolimbic system.

Other nearby areas elicit terror, anger or pain = punichment areas

Question 20

How is the limbic system related to memory?

Answer 20

Limbic system is important in memory

Motivation to learn is to gain a reward or avoid a punishment.
Gives a task significance. Similarly, memory recall depends on association with the significance of an event.

Question 21

What is psychoses?

Answer 21

Group of disorders which represent endogenous inherent malfunction of the brain e.g. schizophrenia and manic depression (bipolar), relationship between behaviour and reward and punishment appears to be impaired

(Neuroses arise as abnormal reaction to external circumstances e.g. phobia and anxiety)

Question 22

How is Neurotransmitter/Neuromodulator involved in behaviour and mood?

Answer 22

Extremely complex and not well understood

Question 23

What is schitzophrenia?

Answer 23

Schizophrenia is a dissociation of the “cognitive” side of behaviour from the “affective/emotional” side of behaviour

There is inappropriate behaviour characterised by episodes of:

• Bizarre delusions, e.g. of being persecuted, of having their feelings thoughts and actions controlled by outside forces
• Auditory hallucinations, hearing voices commenting on their actions
• Disorders of thought, incoherence, loss of the association between ides, poverty of speech and loss of emotional responsiveness.

Question 24

What are classic symptoms of extreme schizophrenia?

Answer 24

Incoherent thoughts, strange meaningless behaviours, paranoia, heightened emotions, delusional, hears voices commenting on his behavious, and directing his thoughts and actions.

“Tardive dyskinesia” manifest by possibly constant twirling of hair is a side-effect of anti-schizophrenic medicine.

Many patients respond to well to medication

Question 25

Explain drugs that control schizophrenia

Answer 25

Drugs that have the greatest effect in controlling schizophrenia generally interfere with dopamine transmission, mainly by blocking DA receptors, used to be thought that is was D2 receptors, D4 now implicated.

N.B. Basal ganglia connection:
-Drugs that interfere with DA -> Parkinsonism

Also schizophrenic like psychotic disorders can be produced by long term use of drugs that enhance DA action e.g. amphetamine, increases DA, release, Cocaine decreases DA breakdown (and L-DOPA)