Week 6 (Module 7-8)

Question 1

Early entrainment experiments on humans, conducted by ______, showed _______

Answer 1

• Aschoff & Wever

- Humans are less sensitive to light as a time cue, and that social cues are more effective

Question 2

What problem was found with Aschoff & Wever’s experiment?

Answer 2

Subjects were allowed to use reading lights even when the overhead lights were off, so they were able to create their own LD cycle

Question 3

What did Czeisler find when studying humans kept in a strictly enforced LD cycle?

Answer 3

Humans entrained to the cycle

Question 4

Pineal melatonin secretion is controlled by ______, and is not affected by _____

Answer 4

• The circadian clock

- Sleep-wake cycles

Question 5

When does melatonin rise, peak, and fall?

Answer 5

• Rises in the evening, prior to sleep onset
• Peaks in the middle of the night
• Falls in the morning, near wakeup time

Question 6

Melatonin secretion is rapidly suppressed by ____

Answer 6

Light

Question 7

In humans and nocturnal animals, a light pulse early in the subjective night causes a ______, while a light pulse late in the subjective night causes a ______

Answer 7

• phase delay

- phase advance

Question 8

Where is melatonin synthesized and secreted?

Answer 8

The pineal gland

Question 9

Blind people with functional retinal photoreceptors continue to show ______

Answer 9

Light-induced melatonin suppression

Question 10

Dim-light melatonin onset is typically defined as _______

Answer 10

The time when melatonin levels reach 25% of the maximum value that it eventually exhibits

Question 11

Failure of circadian blind people to entrain to a fixed sleep-wake schedule implies that _______

Answer 11

Non-photic stimuli are weak in humans or not controlled enough to produce stable entrainment

Question 12

Tau in sighted people is an average of ____, while in blind people the average is _____

Answer 12

• 24.25h

- 24.6h

Question 13

What is a possible reason why it is harder to entrain to a 24h clock via non-photic stimuli in blind people than sighted people?

Answer 13

Tau for sighted people is closer to 24h, so there is less need for a strong effect of the stimuli

Question 14

What effect does cohabitation seem to have on circadian rhythms in humans?

Answer 14

Synchrony in light, but asynchrony in constant dark

Question 15

1 hour of exercise in the morning or at night can ____ the internal clock, while in the evening it can _____

Answer 15

• phase delay

- phase advance

Question 16

Scheduled sleep-wake without exercise can cause a _____, but is a weak ____

Answer 16

• shift advance

- zeitgeber

Question 17

What is considered the gold-standard circadian phase marker in humans?

Answer 17

Melatonin levels

Question 18

Daily exercise schedules can facilitate _____

Answer 18

Entrainment to different sleep-wake cycles

Question 19

Data on how food affects human rhythms is _____

Answer 19

very limited

Question 20

What elements must a model of the circadian system contain?

Answer 20

• Pacemaker to entrain LD cycles
• Pacemaker to entrain feeding cycles
• Photic input to the clock
• Inputs associated with food/arousal
• Clock outputs

Question 21

To account for splitting, a model needs to represent entrainable pacemakers as ______

Answer 21

coupled oscillators

Question 22

Master pacemakers send signals to ______

Answer 22

local oscillators

Question 23

What is spontaneous internal desynchronization?

Answer 23

Days lengthen for humans kept in constant dark, indicating desynchrony between the sleep-wake cycle and body temperature