PSYCHOBIOLOGY OF

ALTERED STATES OF AWARENESS

Circadian Rhythms

www.aperfectworld.org/ cartoons/sleep.gif

One major determiner of biological sleep propensity - Sleep Homeostasis

A second major biological determiner of sleep propensity -

Circadian Rhythms (circa=about, dian=day,24hrs)

Circadian Rhythms• They are ubiquitous.

Virtually every physiological, hormonal, and behavioural measure taken across time will show a circadian rhythm.

• Most are endogenous, not driven by behaviour/sleep but having an effect on behaviour/sleep.

More Circadian Rhythms

• Subjective sleepiness• Plasma Glucose• Core body (rectal)

temperature• Plasma Cortisol• Plasma Melatonin• Plasma thyroid stimulating

hormone (TSH)• Peak values for the

different rhythms occur at different times in a normally entrained individual.

Circadian Core Temperature and Sleep Propensity

Circadian Rhythms and Sleep out of Synchrony

• Night Shift work, work at night is difficult and prone to error. Sleep during the day is difficult and not adequate.

• Jet Lag. Flying across time zones can result in attempt to be awake when your circadian clock is primed for sleep. Sleep at your destination night time can be difficult because your body is primed for arousal and activity.

• Certain types of insomnia?

Individual DifferencesMorning versus Evening Types

• Eve. types went to bed and woke later.

• Evening types had a melatonin rhythm 3 hours later than Morning types.

• They also had later temp., sleep propensity, and particularly later subjective sleepiness

On all circadian rhythms Evening types were later than Morning types

What happens to the sleep of evening and

morning types if forced at different

bed times?

• Early to bed for E types results in difficulty falling asleep.

• Late to bed for M types results in difficulty maintaing sleep.

Development of Insomnia

• Delayed rhythms can result in sleep onset insomnia, common in younger people.

• Advanced or early rhythms can result in early morning awakening insomnia.

• Treatment to re-time the body clock may be therapeutic.

Delayed and Advanced Sleep Phase Syndromes Extreme examples of

SOI and EMA insomnia

Re-timing the Body Clock with Bright Light

• The body clock is the suprachiasmatic nucleus (scn).

• It controls the timing of the circadian rhythms and sleep propensity.

• It can be re-timed with bright light.

• Bright light in the evening delays.

• Bright light in the morning advances the body clock.

Conclusions

• A major determiner of sleep propensity is the circadian system.

• If Sleep/wake becomes de-synchronised with respect to the circadian system, it will be detrimental to sleep and wakefulness.

• Individual differences of evening and morning types is based on later and earlier rhythms.

• Late or early rhythms can lead to insomnia, DSPS and ASPS.

• The controlling body clock is the scn.• Bright light can re-time the body clock and

treat circadian rhythm difficulties.

Application EssayScenario: • Jason is having some difficulty at school because of tiredness, difficulty

maintaining concentration, and poor memory. These problems are especially noticeable in the first couple of hours of school every day. As a result his academic performance is likely to suffer and his grades will be less than his capabilities which in turn will jeopardise his future choices.

• Jason is much more lively late at night and prefers staying up late for social engagements or when he has to do school work. When he has tried going to bed early he is frustrated by not being able to get to sleep. As a result when he has to get up early to get to school he usually gets less sleep than he needs.

• On the weekend he sleeps in to late morning or early afternoon attempting to catch up on sleep. It is probably not surprising he has difficulty getting to sleep before midnight on Sunday night.

• What actions could be taken to improve Jason's ability to get to sleep at night and his alertness during the day?

• When describing your intervention, explicitly state the biological processes which may be contributing to his problems with getting to sleep in the evening and his tiredness in the morning.

• What is the likely outcome of the procedure you have designed? Are there other factors which might need to be taken into account to achieve the desired outcome?

• Consider the ethical issues raised by your intervention. What steps could you take to ensure that these were minimised?