Brain Rhythms: EEG, Sleep and Diurnal Rhythms

Question 1

What is an electroencephalogram?

Answer 1

A measurement of the collective electrical activity of the neurones in a particular region of the brain.

Question 2

Why is EEG only effective for detecting cortical activity?

Answer 2

Because electrodes must be placed on the surface of the patient, so only surface electrical activity can be measured effectively.

Question 3

What might be seen on an electroencephalogram in a patient with epilepsy?

When might this phenomenon be seen in individuals without epilepsy?

Answer 3

• In patients with epilepsy, there is sudden abnormal synchronisation across all inputs from the electrodes.
• Synchronisation occurs outside of epilepsy in:

1 - Cognition, particularly pattern recognition.

2 - Sleep.

Question 4

Define sleep.

Answer 4

A readily reversible state of reduced consciousness.

Question 5

List the stages of sleep.

Answer 5

1 - REM sleep.

2 - Stages 1-4 of non-REM sleep.

Question 6

What changes with the stages of non-REM sleep?

Answer 6

There is increased synchrony with later stages of non-REM sleep (greater synchrony towards stage 4).

Question 7

List 5 characteristics of REM sleep.

Answer 7

1 - Rapid darting eyes.

2 - Easily aroused by meaningful stimuli.

3 - When awakened, appear alert and attentive.

4 - Dreaming.

5 - Loss of muscle tone.

Question 8

Describe the normal pattern of sleep stage progression during sleep.

Answer 8

1 - Initially, sleep begins at REM then oscillates down and up the stages of REM and non-REM sleep.

2 - Sleep stages become less deep as sleep progresses (e.g. only reaching stage 2 at maximum rather than stage 4).

3 - Periods of brief awakening start to occur between cycles.

4 - REM sleep increases in duration.

5 - Sleep ends.

Question 9

Which network of nerves is thought to form part of the neural basis of wakefulness?

Where is this structure located?

Answer 9

• The reticular activating system.

- It is located in the brainstem.

Question 10

How does the reticular activating system contribute to wakefulness?

Answer 10

• Sensory information in ascending tracts and motor information in descending tracts to / from the brain pass through fibres of the reticular activating system to the thalamus.
• The neurones of the reticular activating system use ACh and aminergic neurotransmitters at the thalamus to allow this information to be passed to the cortex via this order sensory neurones.

Question 11

Why does REM sleep appear similar to wakefulness on an electroencephalogram?

Answer 11

Because, similar to wakefulness, the neurones of the reticular activating system carrying sensory information also use ACh (but not aminergic neurotransmitters) during REM sleep, allowing some sensory information to pass to the cortex.

*This is why REM is also more similar to wakefulness than sleep beyond electroencephalograms.

Question 12

Why can antihistamines cause drowsiness?

Answer 12

Because histamine is one of the aminergic neurotransmitters used by the reticular activating system during wakefulness.

Question 13

List 2 physiological changes in the brain that occur with non-REM sleep.

Answer 13

1 - Reduced ACh signalling at the thalamus from the reticular activating system.

2 - Increased aminergic signalling at the ventrolateral preoptic organ (VLPO).

Question 14

Accumulation of which neurotransmitter determines waking time?

Answer 14

Accumulation of adenosine determines waking time.

Question 15

What is the suprachiasmatic nucleus?

Answer 15

A nucleus involved in the control of circadian rhythms.

Question 16

How can the circadian rhythm be reset?

Answer 16

• The circadian rhythm can be reset with light via direct retinal input to the suprachiasmatic nucleus.
• This retinal input is known as a zeitgeber.

Question 17

List 2 features that might be seen on an electroencephalogram in patients with depression during sleep.

Answer 17

1 - A greater proportion of sleep is REM sleep rather than deep sleep.

2 - The patient enters REM sleep much more rapidly.

Question 18

Give an example of a characteristic of REM sleep disorders.

Answer 18

Loss of brainstem inhibition of muscle tone, causing affected individuals to act out dreams.

Question 19

List 3 deep sleep disorders.

Answer 19

1 - Sleep apnoea.

2 - Insomnia.

3 - Narcolepsy.

Question 20

Define narcolepsy.

Answer 20

A sleep disorder characterised by:

1 - Uncontrollable entry into REM sleep.

2 - Cataplexy (loss of muscle control with strong emotion).

Question 21

What is orexin?

How might it be implicated in narcolepsy?

Answer 21

• A substance secreted by the hypothalamus that controls wakefulness by promoting aminergic and cholinergic neurones at the reticular activating system..
• It is secreted in abnormally low levels in narcolepsy.