PSY372 L11 Sleep

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University of Toronto St. George
Kristie Dukewich

PSY372 L11 02/12/2013 Sleep = altered state of consciousness; being in coma, anesthetic; don’t involve external stimuli; can be woke up by whispering your name but not the truck since your name is meaningful to you Dream: most people report no dreaming exp because we forget the content of dream  As of 2008, the American Academy of Sleep Medicine (AASM) has discontinued the use of stage 4, such that the previous stages 3 and 4 now are combined as stage 3.  Awake: Beta-activity = brain activity in bed when trying to sleep; When you’re awake, beta-activity has the highest frequency but lowest amplitude; starts to slow down as you try to sleep  NREM Stage 1: Alpha + Theta activity, hypnogogic hallucination = vivid, weak exp of events but lack narrative structures, related to what you were doing before your sleep; have a feeling of falling o No exp/aware of going from awake to stage 1 of sleep;  NREM Stage 2: A sleep spindle is a burst of oscillatory brain activity visible on an EEG that occurs during stage 2 sleep. Sleep spindles may represent periods where the brain keeps the sleeper in a tranquil state. Along with K-complexes they are defining characteristics of stage 2 sleep; we spend 50% of our sleep in stage 2  NREM Stage 3: SLOW-WAVE SLEEP(SWS) which consists of delta activity - very low frequency, high amplitude, difficult to wake up the sleeper; NREM Stage 4: respond to stimuli in stage 4; wake up to your name; [Stage 3 & 4 combine]  REM sleep: theta & beta activity, awake & alert; paradoxical sleep = the sleeper, although exhibiting EEG waves similar to a waking state, is harder to arouse than at any other sleep stage. Vital signs indicate arousal and oxygen consumption by the brain is higher than when the sleeper is awake. An adult reaches REM approximately every 90 minutes, with the latter half of sleep being more dominated by this stage.  Early sleep: longer periods of slow-wave sleep, shorter periods of REM sleep; later sleep dominated by REM sleep and the proportion of SWS decreases. o Even your sensory cortices are active, since they represent your sensory experience but motor activity is blocked so you don’t act out your dream. o Each wave cycle turns over every 90min; wake up at 45min = stage 2; wake up at 90min = REM; wake up at 30min, feel groggy (weak, unable to think clearly) Functions of sleep  Jenkins & Dallenbach: SS learn 10 non-sense syllables right before bed & woke up at different intervals & see if they remember syllables; 1 PSY372 L11 02/12/2013 o SS in awake condition show a pattern like Ebbinggaus’ retention curve, they forget most of info by 2 hours, BUT SS in sleeping condition preserve memory of syllables; Sleep passively prevents retroactive interference by preventing new info from interfering old info  Souissi et al.: effect of sleep deprivation on anaerobic performance; kept SS awake for 36 hours; o Anaerobic exercise – muscle strength; peak power/max power/mean power/force/velocity o Up to 24 h of waking, anaerobic performance were not affected; however, they were impaired after 36 h without sleep o Sleep deprivation reduced the difference between morning and afternoon in anaerobic power performance. o Memories more related to cog functions, rather than physical  Amedt et al: pediatric residents work either 2 types of shift rotations o Light call = 12 hr shifts, Heavy call = 36 hr shifts; light call + alcohol during light call; test after their shifts o Vigilance task: Press every time they saw a 7;  Light call residents performed significantly better than light+alcohol & heavy call o Continuous performance: press every number except 7; light call > heavy call > alcohol o Simulated driving: light call> alcohol > heavy call, so they shouldn’t drive after their shifts o Major impact of sleep deprivation is cognitive.  Motor sequence learning task (Procedural memory) o SS given series of number 42123 & press them on a number pad with dominant hand o Present digits & train them repetitively & sleep o Behavioral results: normalize everybody’s results; generally people get better gradually upon training; SS got better results through sleep than the control, results are correlated with no. of sleeps given at that night; o There were most fast sleep spindles in stage 2 after the MSL task compared to the control task. o Sleep spindles have a central role in memory consolidation: spindles cement new synapses  The number of spindles have a significant role in declarative memory: o Clemens et al: the number of spindles in stage 2 correlated with verbal free recall of learned names (verbal learning), particularly in frontcentral areas o r-values = correlation = 0.6 in these areas = high  Synaptic consolidation, which occurs within the first few hours after learning 2 PSY372 L11 02/12/2013 Tononi’s synaptic homeostasis hypothesis Learning a bunch of things Then the total → make new synaptic weight synapses → During sleep, returns to low-wave sleep baseline level synaptic comes in & (80,120 left); Number of potentiation promotes synapses (100,150,5); synaptic synapses This leads to a downscaling. contributingto present NET ↑ in the noise < when we synaptic weight contributingto wake up = Slow-wave sleep the signal onto neurons baseline (100,150,5); downscale every Result: ↑ (100,100) > Your brain gets synapse by a signal/noise crowded; proportional ratio, energy energy costs, amount, say saving, space 20%, savings &, what space costs, you learn brain becomes stands out; saturated. Analogy = Background becomes more silent since other things in the surroundings have gone in volume. At the end of the day, the things you need to know left standing. [The higher the amount of synaptic potentiation in cortical circuits during wakefulness, the higher the increase in slow-wave activity during subsequent sleep]  Number of synapses present when we wake up in the morning = baseline (100,100)  Learning a bunch of things → generate new synapse → synaptic potentiation (100,150,5); long-term potentiation-related changes in the cortex during wakefulness lead to a net increase in synaptic weight onto neurons (100,150,5); your brain gets crowded; energy costs, space costs, brain becomes saturated.  During sleep, low-wave sleep comes in & promotes synaptic downscaling. Slow-wave sleep downscale every synapse by a proportional amount, say 20%, then the total synaptic weight returns to baseline level (80,120); synapses contributing to the noise are weaker than those contributing to the signal, result: ↑ signal/noise ratio, energy saving, space savings &, what you learn stands out;  Slow-wave sleep decreases, consolidate what your learn → Whatever theory of consolidation you prefer, both postulate that establishment of long-term memories requires off-line reactivation. New things you learn need to be continuously reactivated  Wilson & McNaughton: cell-pair 1 fire at a particular location; different cell pairs fire at different places, high co-activation; during the task, firing correlated with receptor field; during sleep, firing in the same 3 PSY372 L11 02/12/2013 pattern as they are running the maze but in a compressed time scale. Firing happens multiple times during sleep. Hippocampal place cells exhibit signs of memory reactivation during sleep.  Smith & Weeden: SS learn complex logic task (algebra with new rules) in the presence of a loud ticking clock; during subsequent sleep, one group is cued with the ticking sound & the control isn’t. During the test phase, SS perform the complex logic task. People who were cued with a ticking sound during subsequent sleep improved by 23%, compared to no improvement for the uncued group o Ticking clock triggered reactivation of learning, similar to encoding specificity Functions of dreaming  We exp sth during the day, dreaming is related to hypnogogic hallucination  SS being woke up during REM sleep → dream, a product of activating & reactivating particular synapses, things we encounter that day  Stickgold et al: 3-D virtual space, ask SS to create map & train them a lot; SS take a 90-min nap o Sleeping group: What were you dreaming about? Control: what were you thinking about? o In the s
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