aula de ciclos circadianos I

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SLEEP
Chapter 14
Why do we sleep?
Why do we dream – what do dreams mean?
Why do we get sleepy around the same time every day?
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OVERVIEW	
Stages of sleep
Stage 1, stage 2, stage 3, stage 4
REM sleep and dreaming
Theories of sleep
Recuperation theories of sleep
Circadian theories of sleep
Circadian sleep cycles
Effects of sleep deprivation – humans
Effects of sleep deprivation – animals
REM-sleep deprivation
Sleep deprivation - SWS
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3 STANDARD PSYCHOPHYSIOLOGICAL MEASURES OF SLEEP
There are certain physiological events, both neurally and physically, that accompany sleep
Measure with
– EEG – neural events
– EOG – eye movements
– EMG – muscle tension
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EEG - ELECTROENCEPHALOGRAM
Large disk electrodes on the scalp record electrical potentials
extracellular voltage changes over a relatively large area of cortex (~ cm)
Useful - major changes in EEG during the course of a night’s sleep
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STAGES OF SLEEP
Alert – low amplitude, high frequency
Drowsy – similar to alert, but occasional alpha waves (8-12Hz, slightly higher amplitude)
Stage 1 – similar to alert, but slower and higher
Amplitude
Stage 2 – similar to stage 1, but occasional sleep
spindles (1-2s burst of 12-15Hz) and K-complexes
(large negative followed by large positive deflection)
Stage 3 – slower, larger, occasional delta spikes (large1-2Hz bursts)
Stage 4 – predominance of delta
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GOING THROUGH THE STAGES 
Descend through stages sequentially
Get to stage 4 within 45 minutes
Eventually start going back up to stage 1, keep going up and down throughout night
Returns to stage 1 are called “emergent” and are characterized by rapid eye movements (REM)
REM
Loss of core muscle tone
Low-amplitude, high frequency EEG
Cerebral activity (oxygen consumption, blood flow, neural firing) increases to waking levels
General increase in autonomic NS (bp, pulse)
REM periods typically 90 minutes long
As night goes on, spend less time in lower stages, brief periods of wakefulness not remembered in morning
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REM AND DREAMING
80% of awakening from REM sleep (only 7% from NREM) led to dream recall
Dreams during NREM – isolated experiences (i.e.falling)
Dreams during REM – stories
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CHARACTERISTICS OF DREAMING	
External stimuli can become incorporated into dreams
Dreams run on “real time”
Everyone dreams – to some degree
Erections occur during dreams – regardless of content
Sleeptalking occurs during a transition to wakefulness
Sleepwalking does NOT occur during dreaming
WHY????
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INTERPRETATION OF DREAMS
Freud – dreams are triggered by unacceptable repressed wishes, often sexual	
Manifest dreams – disguised versions of our real dreams (latent dreams)
Key to understanding people and dealing with their psychological problems is to expose the meaning of their latent dreams
Activation-synthesis theory
Information supplied to the cortex during REM sleep is largely random and that the resulting dream is the cortex’s effort to make sense of these random signals.
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WHY DO WE SLEEP, WHY DO WE SLEEP WHEN WE DO?
All animals sleep – sleep is important
All animals sleep – sleep is not a special higher-order human function
Although sleep may be necessary, not necessarily needed in large quantities
No correlation between animal size (level of activity, body temperature) and the amount of sleep
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Why do we sleep? 
Why do we sleep when we do? 
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RECUPERATIVE THEORY
Being awake disrupts homeostasis.
Sleep is required to restore it.
	Homeostasis – the stability of an organism’s internal environment
Therefore, sleep deprivation should produce harmful effects
Problems – What is the internal imbalance?
			 How does sleep restore balance?
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CIRCADIAN THEORY 
Fact: Sleep/Wake cycle follows a circadian rhythm.
Circadian: any physiological or behavioural rhythm with a period of ~ 24 hrs
Theory: Function of Sleep
Sleep evolved in response to the day/night, light/dark cycle, as a way to keep an animal out of harm’s way.
Sleep/wake cycle is analogous to the seasonal rhythm of hibernation (e.g. in bears)
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CIRCADIAN THEORY
In contrast to recuperative theory, it suggests that sleep evolved as an adaptive response to the external day/night cycle, not as a response to some internal physiological signal.
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CIRCADIAN SLEEP CYCLES
Circadian cycles are kept on once-every-24-hours by temporal cues in environment
Light/dark cycle
Zeitebers - environmental cues (light/dark cycle) that can entrain circadian rhythms 
Free-running rhythms - circadian rhythms in constant environments
>24 hours
Not learned
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SLEEP DEPRIVATION
Moderate amounts of sleep deprivation (3-4 hours in one night)
Increased sleepiness
More sleepy	
Fall asleep more quickly
Disturbances on various written tests of mood
Perform poorly on tests of vigilance
Cognition
No consistent effects
Physical performance
no real effects
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SLEEP DEPRIVATION IN LABORATORY STUDIES
Carousel apparatus
Experimental group – died
Control group – healthy
Stress – swollen adrenal glands, gastric ulcers, internal bleeding
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REM-SLEEP DEPRIVATION
Greater tendency to initiate REM sequences
REM rebound - more than usual amount of REM sleep
Function??
Memory
Tricyclic antidepressants
Default state
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IMPORTANCE OF SWS
Following sleep deprivation
Although subjects only regain a small proportion of total sleep loss, regain most of their lost SWS (stages 3 &4)
SWS – higher proportion of slow waves
Short sleepers normally get as much SWS as long sleepers
If subjects take an extra nap in the morning after full nights sleep, naptime EEG shows few SW and the nap does not reduce the duration of the following night’s sleep
Gradual reduction in sleep – no reduction in SWS
Repeatedly waking during SWS – major effects
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A cycle is ~ 90 mins, containing 20-30 mins of REM sleep
Most of stage 3 & 4 occurs during 1st 2 cycles.
Recuperative function: it should be possible to reduce sleep to 6 hours per night and still obtain nearly all the recuperative benefits of sleep.
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