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Lecture 11

Psych 2220A Lecture 11

9 Pages

Course Code
Psychology 2220A/B
Scott Mac Dougall- Shackleton

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Psych 2220A Lecture 11 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 rhythmicity 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 SCN • Is the SCN the master clock in humans? • PatientA.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 –Aform 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 BMAL and CLOCK • 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 Stages of Sleep • How is sleep measured? – In 1950s discovered there are eye movements in certain stages of sleep, and varying EEG activity – Combined measures in sleep labs typically include EEG, EOG, EMG Three Standard Physiological Measures of Sleep • Electroencephalogram (EEG) – Reveals “brainwaves” • Electrooculogram (EOG) – Records eye movements seen during rapid eye movement (REM) sleep • Electromyogram (EMG) – Detects loss of activity in neck muscles during some sleep stages Stages of sleep •Alert: low voltage, high frequency waves • Going to sleep: appearance of alpha waves • Enter sleep: EEG has higher voltage, lower frequency Stages of Sleep • Stage 1 – Higher amplitude and lower frequency • Stage 2 – Punctuation of sleep spindle and K- complex wave forms • Stage 3 – Occasional delta waves • Stage 4 – Dominated by delta waves Psych 2220A Lecture 11 • Rest of night spent going back and forth between stages 1 to 4 • Re-entering stage 1 associated with REM (rapid eye movements) but deeply relaxed muscles • REM sleep: emergent stage 1 EEG sleep • Slow-wave sleep (SWS): stage 3-4 sleep REM Sleep and Dreaming • 80% of awakenings from REM yield reports of story-like dreams • External stimuli may be incorporated into dreams • Dreams run on real time • Everyone dreams • Penile erections are not a result of erotic dreams • Sleepwalking and talking are less likely to occur while dreaming Interpretation of Dreams • Freud postulated dreams are caused by repressed desires – But no evidence to support this (or most of Freud’s other ideas....) •Activation Synthesis Hypothesis – Brain-stem circuits active in REM sleep – Information supplied to cortex is largely random – Dreams a result of cortex trying to integrate and make sense of largely random input Why Do We Sleep? • We are highly motivated to sleep, but why? •Avariety of hypotheses 1) Recuperation theories 2)Adaptation theories Psych 2220A Lecture 11 Recuperation Theories • Idea that sleep is required to restore homeostasis and recuperate from being awake – E.g. restore energy levels? Adaptation theories • Part of a circadian activity cycle • Imposes rest at times of day as a result of adaptation – E.g. diurnal animals sleep at night to avoid injury or predation, and/or to conserve energy •Adaptation theories posit we should be highly motivated to sleep even if we don’t need it to survive (like sexual behaviour) Comparative Studies • Sleep differs from torpor and hibernation • Torpor and hibernation involve lowered metabolic rates – Often animals come out of hibernation to sleep! • Though few species studied it looks like all birds and mammals sleep – But varied amounts (Table 14.1) • Sleep may serve an important recuperative or other function •Animals balance costs and (potential) benefits of sleep • Prey animals like ungulates sleep very few hours • Dolphins do not exhibit REM sleep, and only half of the brain engages SWS at a time – Risk of drow
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