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Lecture 9

Lecture 9 - Behavior Rhythms & Sleep and Emotions

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University of Toronto St. George
Franca Placenza

Biological Rhythms 1. Our behavior seems to occur rhythmically (circadian rhythms) o Also can depend on the time of day and species in question 2. Circadian rhythms - functions of a living organism that display a rhythm of about 24 hours o EX = sleep-wake, activity, hormone levels, body temperature 3. Circadian rhythms are even maintained without external cues o Hamster is ideal animal model to study Studied with an actogram External cues help animal determine when to start running We can manipulate the stimulus (light) to measure hamsters circadian rhythm Implies that the animal has an internal biological clock Light an example of a zeitgeber (time giver) >> the cue that an animal uses to synchronize with the environment o Humans not so much Neurobiology of Circadian Rhythms 4. Suprachiasmatic nucleus (SCN) of the hypothalamus o Can synchronize all the rhythms o Super biological clock o Lesions of this area abolish circadian rhythms in animals (no pattern anymore) 5. When SCN is lesioned in hamsters under constant light condition, there is absolutely no pattern in their rhythm of running 6. Transplantation of SCN restores rhythmicity 7. Hamster mutation discovered called tau mutation o Normal hamster circadian rhythm = 25 hrs o Hamster with tau mutation circadian rhythm = 20hrs 8. After hamster with normal circadian was implanted with SCN with mutation, the hamsters circadian rhythm reduced to 20 hrs (the same as the hosts) SCN receives input from the visual system o Circadian rhythms are entrained by light o In mammals, light info goes from eye to the SCN via the retinohypothalamic pathway 9. 90% of ganglion cells send axons to lateral geniculate nucleus 10.Specialized retinal ganglion cells projecting to SCN contain the light-sensitive pigment, 11.Blindness of any sort in animals doesnt affect their SCN and light is able to entrain them 12.The metabolic activity of the SCN is clock-like o Dark >> low activity of SCN
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