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Lecture 11

Psychology 2220A/B Lecture Notes - Lecture 11: Lesion, Executive Functions, Hypersomnia

Course Code
Scott Mac Dougall- Shackleton

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Organization of Behaviour
• Daily Organization
– Foraging, resting, courtship, hatching
– Terms: nocturnal, diurnal, crepuscular
Annual Organization
– Migration, breeding, hibernation
• Other Cycles
– e.g. tidal rhythms, lunar cycles
Biological Rhythms
Biological rhythms are regular fluctuations in a living process
Circadian rhythms have a rhythm of about 24 hours
Ultradian rhythms such as bouts of activity, feeding, and hormone release repeat more than
once a day
Infradian rhythms such as body weight and reproductive cycles repeat less than once a day
• e.g. menstrual cycle, annual cycle
Circadian Sleep Cycles
• Circadian rhythms – “about a day”
• Virtually all physiological, biochemical, and behavioral processes show some circadian
Do Endogenous Clocks Exist?
• Hold animals in constant conditions
– Exhibit free-running rhythms
– Slightly longer than 24 hours
– Individuals have slightly different rhythms, and become de-synchronized
– Thus, must be endogenous control
Circadian Clock
• Synchronized by environmental cues – time-setters or zeitgebers
– E.g. light, food availability
• Large shifts of clock can take several cycles to entrain
Jet Lag and Shift Work
Jet lag – zeitgebers are accelerated or decelerated
Shift work – zeitgebers unchanged, but sleep-wake cycle must be altered
• Both produce a variety of deficits
• Can the effects be prevented or minimized?
Reducing Jet Lag
• Gradually shift sleep-wake cycle prior to travel
Administer post-flight treatments to promote the needed shift
Psych 2220A Lecture 11
– Exposure to zeitgebers will lead to more rapid entrainment
• Bright sunlight
• Exercise
• Meals
Where is the endogenous circadian clock?
• Many tissues exhibit endogenous rhythms.
• Suprachiasmatic nuclei (SCN)
– Master clock in mammals
Where is the clock?
• Many tissues exhibit endogenous rhythms.
• Suprachiasmatic nuclei (SCN) – master clock in mammals
• Lesion SCN leads to arrhythmia
• Transplant SCN reinstates normal rhythm
• Transplant mutant SCN (approx. 20 h cycle) instates mutant rhythm
• Is the SCN the master clock in humans?
• Patient A.H. received SCN damage during surgery
Psych 2220A Lecture 11
Neural mechanisms of entrainment
• In mammals (but not other animals)
– Light from the eyes entrains circadian rhythm
– NON-visual photoreceptive cells project via retinohypothalamic tract to SCN
A form of retinal ganglion cells with melanopsin as photopigment
Molecular basis of the clock
• Highly conserved between fruit flies and mammals
period (PER) and timeless (TIM) genes key players
Molecular Basis of the Clock
• BMAL and CLOCK genes activate other genes (PER and CRY)
• Protein products of PER and CRY dimerize, reenter nucleus, inhibit further transcription of
• Protein products turn off their own production
Endogenous clock and sleep
• Endogenous clock > 24 hrs
• Typically we want to stay up later and sleep in
• Explains why phase delay has more rapid entrainment
Psych 2220A Lecture 11