Sleep (Lecture 10) Flashcards
What is sleep?
- a readily reversible state of reduced responsiveness to , and interaction with the environment
- not readily reversible:
- coma
- general anesthesia
- death
- —> these do not qualify as sleep
EEG (electroencephalogram
- general activity of the cerebral cortex
- fluctuations in voltage between any given 2 electrodes
- = excitation of cortical neurons
- because signal must penetrate so many layers of non neural tissue = thousands of neurons must fire in unison to generate visible signal
wakefulness and stages of sleep are characterized by…..
-different patterns of brain activity
Awake and Alert
- Beta activity
- 13-30 Hz
- desychronized
Awake and Relaxed
-Alpha activity
8-12 Hz
-increasing synchronicity
-more prevalent with eyes closed
Stage 1 Sleep
-theta activity
-3.5-7.5 Hz
-transition between sleep and wakefulness
eyelids slowly open and close and eyes roll up and down
LASTS ABOUT 10 minutes during first sleep cycle
Stage 2 Sleep
-some theta activity
-3.5-7.5 Hz
-sleep spindles
-12-14 Hz (beta-eque)
-short bursts 2-4 per minute
-K complexes
-sudden sharp waveforms
-1 per minute
-triggered by noises = mechanism to inhibit waking?
LASTS ABOUT !% minutes during first sleep cycle
Slow Wave sleep (SWS)
-Delta activity
< 3.5 Hz
-difficult to wake people from SWS and when awakened, report no dreaming, but may remember image or emotion
Stage 3 sleep
-some theta activity
-20-50% delta
~20 minutes in first sleep cycle
stage 4 sleep
-some theta activity
> 50% delta
-deepest sleep
~ 45 min in first sleep cycle
Delta Waves
-show oscillations of ~1 Hz
down state
- neurons are silent
- may reflect rest for cortical neurons
up state
-neurons show burst of activity that is highly synchronized
REM sleep
- theta activity (like stage 1,2,2)
- 3.5-7.5 Hz
- Beta activity (like wakefulness)
- 13-30 Hz
- Paradoxical Sleep
- people awakened easily from REM sleep and report vivid dreams
Paradoxical SLeep
-EEG shows desychronized brain activity reminiscent of wakefulness
Sleep Cycle
- sleep alternates between REM and nREM (stages 1-4) in 90 minute sleep cycles
- in avg. 8 hours of sleep you experience 4-5 bouts of REM sleep
- as night progresses stage 2 and REM sleep are prolonged and SWS is reduced
Stage 1 physiological changes
- muscle activity reduced
- occasional muscle twitch
Stage 2 Physiological changes
- breathing and heart rate slows
- decrease in body temperature
SWS Physiological changes
- slow rhythmic breathing
- limited muscle activity
REM Physiological changes
- rapid eye movement
- muscles relax
- breathing is rapid and shallow
- heart rate increases
- sexual tissue engorges
Rate of blood flow during REM
- high in visual association cortex
- hallucinations/dreams?
- low in primary visual cortex
Eye movements during REM
-seem to match eye movements that would be made while watching their dream
Particular brain activity during dreams
- cortical and subcortical motor mechanisms active when dreams involve movement
- temporal lobe activity when dreams involve speech
Why do we sleep? Adaptation view
-sleep gives organism safety from danger or predation when they are not suited to puse food or other biological needs
Why do we sleep? Not necessarily for adaptation view
- Indus dolphin of Pakistan
- this dolphin does not sleep in a safe place with no predation
- dolphin can not stop swimming while sleeping because of dangerous current and debris
- sleeps 7 hours per day via 4-60 second microsleeps
Why do we sleep? general view
- not just to rest our bodies
- sleep deprication does not interfere with ability to exercise
- sleep might rest the brain
- sleep deprivation affects cognitive abilities
- perceptual distortions
- hallucinations
- trouble concentrating
- sleep deprivation affects cognitive abilities
What is most important for optimal brain activity?
- slow wave and REM sleep
- these stages comprise more of total sleep following deprivation
Brain resting during sleep
- tasks that require concentration increase glucose utilization in the frontal lobes
- slow wave activity is greatest in frontal lobes during nREM sleep
Huber et al. (2004)
-people that learned a motor task just before going to sleep showed heightened slow wave activity in cortex activated by task
What can aid the consolidation of memories?
SLEEP!
declarative memories
- things you can describe
- events
- spatial relationships
Non-declarative memories
- things learned through experience
- how to drive a car
- recognize a face
REM is important for the consoliation of what type of memory?
-non-declarative
EXPERIMENT
Participants learned non-declarative visual discrimination task
1. one group allowed a 90 minutes nap (EEG used to determine who got REM sleep)
2. other group allowed no nap
tested 9 hours later resulted in:???????
- subjects without nap performed worst
- subjects with only slow wave sleep performed the same as before
- subjects that entered REM performed significantly better
EXPERIMENT
Participants learned a list of words (declarative) or trace a pattern on paper while looking in a mirror (non-declarative)
1. one group allowed a 1 hour nap 9 with no REM)
2. other group was not allowed a nap
tested 6 hours later, results: ????????
- slow wave sleep increase performance on declarative task but not non-declarative task
- —>need slow wave sleep in order to consolidate memories!!!!!
Sigmund Freud (1856-1939)
- dreams are tiggered by unacceptable repressed wishes (usually sexual)
- psychoanalysis involved dream interpretation to expose and confront patients subconscious “wishes”
Activation-Synthesis Theory (Hobson 1989)
- during REM brain stem circuits (pons) become activated and send information to cortex
- cortex takes “random” activations and tries to compose a cohesive story
Neurobiology of Sleep
- two areas of the hypothalamus have problems if excessive sleep or difficulty sleeping is observed
- Discovered by Constantin von Economo during WWI outbreak of encephalitis lethargica
excessive sleep
- lisions of the posterior hypothalamus
- involved in wakefulness
difficulty sleeping
- lesions of the anterior hypothalamus
- involved in falling sleep
reticular formation
- structure in the brain stem that sends projections to thalamus and cortex
- electrical stimulation of reticular formation awakend sleeping cats
lesions in reticular formation
-disrupted sleep-wake cycles
low activity in reticular formation
-produces sleep
high activity in reticular formation
-produces wakefulness
caudal RAS nuclei
- control various aspects of REM sleep
- muscle paralysis
- rapid eye movement
- limb twitches
- EEG desychronization
What percentage of people report significant sleep related problems?
30%
Insomnia
all disorders of initiating and maintaining sleep
- most cases drug-related
- sleep apnea (cessation of breathing during sleep)
- restless leg syndrome = tension in legs that disrupts sleep
Narcolepsy
- 1/2000 people
- severe daytime sleepiness and brief (10-15 minutes) daytime sleep episodes
- may result from genetic mutation in a gene related to orexin
Cataplexy
- recurring loss of muscle tone during wakefulness
- often triggered by strong emotion
- may stem from abnormality in mechanisms that mediate REM
Narcoleptics
- go straight into REm when they fall asleep
- experience sleep paralysis = paralysis just as falling asleep
- hypnogogic hallucinations = dreamlike states during wakefulness
orexin
- neurotransmitter in neurons of the posterior hypothalamus which project all over brain
- reduced orexin in CSF of narcoleptics
- important in wakefulness!
sleep paralysis
- period of inability to perform voluntary movements either at sleep onset or upon wakening
- may be accompanied by visual and/or auditory hallucinations and even “out of body” feelings
