Human Rhythms

Lectures 20 & 21

2 main reasons studying circadian rhythms in humans is difficult?

1. inability to use constant dark

2. teasing apart exogenous & endogenous influences

3 main types of conditions used in circadian rhythm studies?

1. free choice LD cycle

2. forced non-24 hour cycle

3. constant routine

How was Trump’s twitter activity used to determine his sleep schedules?

looked at the time of all of his tweets; determined which phone was likely his; plotted them out; determined peak times & non-active times to determine when he was probably asleep

What interesting finding came out of examining Trump’s twitter activity & speech content?

had the most negative emotional content the day following a late night twitter rampage

How were a lot of the early experiments on human free-running cycles conducted?

scientists would enter caves in isolation

Kleitman & Richardson spent 32 days in a cave trying to entrain to a 28 hour day. What were the results? What did this suggest?

1. younger man adapted his sleep/wake & body temperature cycles well to the 28 hour day; older man did not

2. showed that the core body temperature rhythm was inate

Siffre spent 62 days in a cave to determine the human free-running period. What period did he free-run at?

24.5 hours

Lobban & colleagues lived in isolated Arctic island over the summer solstice (24 hour daylight) & slept in blackout tents. They messed with their watches, running anywhere between 21-27 hours (outside limits of entrainment). What were the results?

some physiological variables followed sleep/wake; others followed circadian clock

Isolation Apartments

can be in groups/alone in temporal isolation; all the appliances of a normal home, without the clocks; staffed 24/7; either constant light, forced LD, or self-choice LD

4 advantages to studying humans?

1. follow instruction

2. can perform oral & written tests

3. can collect urine, saliva, & blood easily

4. lots of these fluids (allows for repeated samples)

6 disadvantages to studying humans?

1. fussy about isolation

2. lifestyle preferences regarding recreation

3. modern humans are very different from primitive ones in daily needs

4. high costs (constricts sample size)

5. light control

6. ethics

Most physiological systems, such as fussy about isolation _____ _____, _____, and _____ _____, can be influenced by both behaviour & the brain.

1. body temp

2. cortisol

3. waste excretion

How do you determine circadian influences from behavioural ones?

constant routine

Constant Routine

remove contribution of behaviour & environment; stay awake & recumbent for 24-40 hours; fed through IV/many small, identical meals; constant dim light, temp, & humidity

If body temp isn’t influenced by circadian rhythm, what should be see in a constant routine study? What do we see, in practice? What does this suggest?

1. lack of body temp cycling

2. rhythms persist, but body temperature decreases in amplitude

3. some of the body temp is influenced by behaviour, but circadian rhythm also has an influence over the cycle