Physiology of Sleep and EEG

1. PHYSIOLOGY OF SLEEP
AND EEG
Dr. Mohamed Abdelghani
M.B.B.Ch., M.Sc., M.D. Psych.

2. OBJECTIVES:
 By
the end of this lecture, you should
understand:
1)
Difference between sleep & coma.
2)
Why do we sleep?
3)
Mechanism of sleep.
4)
EEG waves
5)
Types and Stages of sleep: (NREM & REM).
6)
Sleep/awake cycle.
7)
Sleep disorders.
8)
Sleep Hygiene.

3. DEFINITIONS
 Sleep:

A state of loss of consciousness from which a
subject can be aroused by appropriate stimuli.
 Coma:

A state of unconsciousness from which a subject
cannot be aroused.

4. WHY DO WE SLEEP? “FUNCTIONS OF
SLEEP”:
1)
Restoration or repair:
 Waking
 Sleep
2)
3)
4)
5)
6)
life disrupts homeostasis
may conserve some energy
Protection with the circadian cycle.
Circadian synthesis of hormones.
Consolidation of learning.
Remodelling of synaptic function.
Dreaming.

5. MECHANISM OF SLEEP
“THEORIES OF SLEEP”

6. WHAT MAKES US FALL ASLEEP?
The old theory of sleep “The passive process”:
I.

Discharging of RAS neurons for many hours of wakefulness
 Fatigue of RAS neurons  Sleep .
The new theory of sleep “The active sleep-
II.
inducing inhibitory process”:

Different mediators actively inhibit the RAS  sleep:
1.
Serotonin-secreting Raphe fibers inhibit the RAS  sleep.
2.
Melatonin “hormone secreted by the Pineal Gland” during darkness
 inhibits RAS  sleep .

7. EEG
WAVES

8. 
The frequencies of brain waves range from 0.5-500 Hz.

The most clinically relevant waves:
1)
Alpha waves - 8-13 Hz
2)
Beta waves - Greater than 13 Hz (18-30)
3)
Theta waves - 3.5-7.5 Hz
4)
Delta waves - 3 Hz or less

9. 1) ALPHA WAVES

Seen in all age groups but are most common in adults.

Most marked in the parieto-occipital area.

Occur rhythmically on both sides of the head but are
often slightly higher in amplitude on the nondominant
side, especially in right-handed individuals


Occur with closed eyes , relaxation, wondering mind.
Disappear normally with attention (eg, mental
arithmetic, stress, opening eyes, any form of sensory
stimulation), then become replaced with irregular low
voltage activity.

10. 2) BETA WAVES
Seen in all age groups.
 Small in amplitude , usually symmetric and more
evident anteriorly.
 Drugs, such as barbiturates and
benzodiazepines, augment beta waves.
 > 13 Hz/sec


11. 3) THETA WAVES
Normally seen during sleep at any age.
 In awake adults, these waves are abnormal if
they occur in excess.
 Theta and delta waves are known collectively as
slow waves.


12. 4) DELTA WAVES
Slow waves, have a frequency of ≤ 3Hz or less.
 Normally seen in deep sleep in adults as well as in
infants and children.
 Delta waves are abnormal in the awake adult.
 Often, have the largest amplitude of all waves.
 Delta waves can be focal (local pathology) or diffuse
(generalized dysfunction).


13. SLEEP SPINDLES
Groups of waves that occur during many sleep
stages but especially in stage 2.
 Have frequencies in the upper levels of alpha or
lower levels of beta.
 Lasting for a second or less, they increase in
amplitude initially and then decrease slowly. The
waveform resembles a spindle.
 They usually are symmetric and are most obvious in
the parasagittal regions.


14. TYPES AND
STAGES OF
SLEEP

15. TYPES OF SLEEP “DEPENDING ON EEG
CRITERIA”
Slow-wave sleep (non-REM):
1.


Stage 2 NREM

Stage 3 NREM

2.
Stage 1 NREM
Stage 4 NREM
Rapid Eye Movement Sleep (REM):

16. DISTRIBUTION OF SLEEP STAGES

17. DISTRIBUTION OF SLEEP STAGES

While NREM occupies about 75-80%, it is interrupted by
intervening REM sleep period.

In a typical night of sleep, a young adult:
I.
II.

First enters NREM sleep, passes through stages 1 , 2 , 3 and 4.
Then goes into the first REM sleep episode.
This cycle is repeated at intervals of about 90 minutes
throughout the 8 hours of a night sleep.

Therefore, there are 4-6 sleep cycles per night (and 4-6 REM
periods per night).

As the night goes on  there is progressive reduction in stages
3 and 4 sleep and a progressive increase in REM sleep .

20. Physiological Changes During NREM and
REM Sleep
Physiological Process
NREM
Brain activity
Decreases from wakefulness
Heart rate
Slows from wakefulness
Blood pressure
Decreases from wakefulness
Sympathetic nerve activity Decreases from wakefulness
Muscle tone
Similar to wakefulness
Blood flow to brain
Decreases from wakefulness
Respiration
Decreases from wakefulness
Airway resistance
Increases from wakefulness
Body temperature
Sexual arousal
Is regulated at lower set point
than wakefulness; shivering
initiated at lower temperature
than during wakefulness
Occurs infrequently
REM
Increases in motor and sensory
areas, while other areas are
similar to NREM
Increases and varies compared
to NREM
Increases (up to 30 percent) and
varies from NREM
Increases significantly from
wakefulness
Absent
Increases from NREM, depending
on brain region
Increases and varies from NREM,
but may show brief stoppages;
coughing suppressed
Increases and varies from
wakefulness
Is not regulated; no shivering or
sweating; temperature drifts
toward that of the local
environment
Greater than NREM

21. SLEEP
WAKEFULNESS
RHYTHM

22. •
Periods of sleep and wakefulness alternate
about once a day.
•
A circadian rhythm consists typically of 8h sleep
and 16h awake.
•
This rhythm is controlled by
1)
The suprachiasmatic (SCN) nucleus “The
Biological clock”: located in in the hypothalamus.
2)
Melatonin release “from the Pineal Body”.

24. SLEEP
DISORDERS

25. SLEEP DISORDERS ARE DIVIDED IN 2 SUB-TYPES
I.
Dyssomnias:
Sleep disorders that are characterised by disturbances in
the amount, quality or timing of sleep.
 E.g.:

Insomnia
 Hypersomnia
 Sleep apnea

II.
Parasomnias:


Dysfunctions or episodic events occurring with sleep.
E.g.:
Sleep-walking (somnambulism)
 Sleep-related enuresis (bedwetting)
 Sleep-talking (somniloquy)
 Sleep-terrors and nightmares


26. Sleep Hygiene
1. Regular, daily physical exercises (preferably not in the evening).
2. Minimize daytime napping.
3. Avoid fluid intake and heavy meals just before bed-time.
4. Avoid caffeine intake (e.g. tea, coffee, cola drinks) before sleeping
hours.
5. Avoid regular use of alcohol (especially avoid use of alcohol as a
hypnotic for promoting sleep).
6. Avoid reading or watching television while in bed.
7. Sleep in a dark, quiet, and comfortable environment.
8. Regular times for going to sleep and waking-up.
9. Try relaxation techniques.