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Sleep
•
o Stage 1
§ Slow theta waves, 4-7Hz
§ ‘light sleep’, would not report being asleep if woken
o Stage 2
§ theta waves with sleep ‘spindles’ of 12-14Hz and K-complexes
o Stage 3
§ Sleep spindles decrease and theta waves become longer and slower
and become delta waves
o Stage 4
§ Very deep sleep, predominantly delta waves
§ brain energy consumption falls to 25% of that recorded during
wakefulness
§ reduced muscle tone
§ increased activity in the parasympathetic NS
o REM sleep
§ Waves similar to wakefulness, combination of alpha, beta and
desynchronised
o More 3 & 4 stage sleep early in night, REM & 2 later
•
5 stages of sleep
Different functions?
o REM
§ Memory storage?
§ Particularly weakening irrelevant connections
§ Motor memory?
o Stage 2
§ Spindles – memory consolidation? Verbal memory?
o Stages 3 & 4
§ Repair and regrow tissue, build bone and muscle, strengthen immune
system
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Sleep deprivation
o Kleitman (1963)
§ 1st night – no sleepiness except between 3 and 6 am
§ Next morning – fine except a bit sleepy when sitting down or not
much stimulation
§ 2nd night – reading or studying next to impossible due to
overpowering need to sleep
§ 3rd and 4th nights – similar to 2nd
§ By the end of the time all had experienced wavelike patterns of
sleepiness and alertness about the same time every day/night
o Dement (1978)
§ Randy Gardner – stayed awake for 11 days
§ During those days showed some difficulties such as fatigue, irritability,
and memory problems
§ By 7th day EEG showed abnormal pattern of alpha waves, but the
symptoms showed consistent fluctuation, and at the end he was
coherent at press conference and beat Dement at a game of penny
basketball
§ He then went to sleep and slept for 15hours, then 10 ½ and then back
to normal with no signs of adverse effects following 11 nights of no
sleep
o Facts about sleep deprivation
§ Fall asleep more quickly when given the opportunity
§ Display disturbances in various written tests of mood
§ Perform poorly on tasks of vigilance
§ Perform poorly on cognitive tasks that involve executive function
(assimilating changing information, updating plans and strategies,
innovative thinking, lateral thinking, insightful thinking) – prefrontal
cortex function
§ No consistent effect on motor function, cardiovascular or metabolic
measures or muscle strength
o REM sleep deprivation
§ Webb & Andrew (1967) – needed to wake subjects up 17 times on
first night, by 7th night had to wake them up more than 67 times
§ After sleep deprivation you try to regain lost slow wave sleep (stages
3 & 4)
§
•
•
Short sleepers normally get as much SWS as long sleepers
Cognitive neuroscience of sleep
o Damage to anterior hypothalamus = wakefulness
o Damage to posterior hypothalamus = excessive sleep
o Caudal reticular formation -> controls REM sleep
o Melatonin – major hormone that affects sleep
Superchiasmatic nucleus
o Determines circadian cycle
§ Richter (1967)
• large medial hypothalamic lesions disrupt circadian cycles of
eating, drinking and activity in rats
§ Ralph et al (1990)
•
•
•
removed the SCN from the foetuses of mutant hamsters that
have short (20hr) sleep-wake cycle
transplanted the SCN into normal adult hamsters (25hr sleepwake cycle) whose SCN was abolished (lesioned)
Results:
o Transplants restored sleep-wake cycle to 20hr
o The SCN is freely determining circadian rhythms