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Chapter 9

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McGill University
PSYC 211
Yogita Chudasama

Chapter 9: Sleep and Biological Rhythms Notes taken by: Ashley Brown Contact for mistakes: [email protected] A Physiological and Behavioral Description of Sleep Sleep is a behavior but not distinguished by movement. Stages of Sleep Sleep is studied in a sleep laboratory - electromyogram (EMG): an electrical potential recorded from an electrode placed on or in a muscle; attached at the chin - electroencephalogram (EEG): record electrical activity of the brain; attached at the scalp - electro-oculogram (EOG): an electrical potential recorded from the eyes, recorded by means of electrodes placed on the skin around them; detect eye movements During wakefulness the EEG of a normal person shows two basic patterns of activity - alpha activity: smooth electrical activity of 8 – 12 Hz recorded from the brain, generally associated with a state of relaxation o more prevalent when eyes are closed - beta activity: irregular electrical activity of 13 – 30 Hz recorded from the brain, generally associated with a state of arousal o the desynchrony shown reflects the fact that many different neural circuits in the brain are actively processing information Stage 1 of Sleep - when we get drowsy and the transition from wakefulness to sleep occurs we show theta activity o EEG activity of 3.5 to 7 Hz that occurs intermittently during early stages of slow-wave sleep and REM sleep - This is a transition phase Stage 2 of Sleep - occurs 10 minutes after stage one - EEG becomes irregular with mixture of theta activity, sleep spindles, and K complexes o Sleep spindles are short burst of waves (12 – 14 Hz) which occur 2 to 5 times a minute during stages 1 – 4 of sleep  The sleep of older people contains fewer sleep spindles  Represents the activity of a mechanism that is involved in keeping a person asleep o K-complexes are sudden, sharp waveforms which are found in stage 2 only. They occur spontaneously at approximately 1 per minute but can be triggered by unexpected noise  Represents an inhibitory mechanism that is involved in keeping a person asleep  Forerunner of delta waves - Even though the subject is sleeping soundly if suddenly awoken they will report that they hadn’t been asleep Slow-wave sleep: collective term for stages 3 and 4 of sleep, characterized by synchronized EEG activity during its deeper stages and predominated by slow-wave EEG activity - 15 minutes later enter stage 3 sleep which is signaled by occurrence of high amplitude delta activity (less than 3.5 Hz) - Stage 3 contains 20 – 50 % delta activity - Stage 4 contains more than 50% delta activity o During stage 4, the deepest stage of sleep, only loud noises will cause them to wake and when awakened the person acts groggy and confused o Cerebral blood flow and oxygen consumption decrease - Most important feature of slow-wave activity during sleep are slow oscillations less than 1 Hz o Each consist of a single high-amplitude biphasic (down and up) wave o First part of the wave indicates a down state – a period of inhibition during which neurons in the neocortex are absolutely silent, and presumably able to rest o The second part indicates an up state – a period of excitation during which neurons briefly fire at a high rate o The other components of SWS like sleep spindles and delta waves are synchronized with these slow wave oscillations o Important for learning and memory - Lack of this sleep affects cognitive abilities rather than physical in humans - Never regain lost SWS after sleep deprivation - SWS is for the brain to restore the effects of oxidative stress About 90 minutes after the beginning of sleep (or 45 minutes after the onset of stage 4 sleep) there is an abrupt change  REM sleep - EEG suddenly becomes desynchronized, with a sprinkling of theta waves, very similar to the record obtained during stage 1of sleep - Eyes rapidly dart back and forth beneath closed eyelids - The EMG becomes silent, there is a profound loss of muscle tone and besides the occasional twitching, muscles are totally inactive during REM sleep - Don’t react to noise but can be aroused by meaningful stimuli - Dreaming occurs during REM sleep. Cerebral blood flow and oxygen consumption increase. - During most periods of REM sleep a male’s penis will become at least partially erect and a female’s vaginal secretions will increase o Independent of sexual arousal - Consolidates memories of events of previous day o In rats, REM sleep facilitates learning During rest we alternate between REM and non-REM sleep, in 90 minute cycles that contain 20 to 30 minute bout of REM sleep - most SWS occurs during the first half of the night - subsequent bouts of non-REM sleep contain more and more stage 2 sleep and bouts of REM sleep become
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