Chapter 34
Electroencephalogram (EEG),
Wakefulness and Sleep
I.I. Electroencephalogram Electroencephalogram (EEG)(EEG)
I. Brain Waves and EEGI. Brain Waves and EEG
Normal brain function involves continuous electrical activity Brain Wave
– The undulations in the recorded electrical potentials– Change with age, sensory stimuli, brain disease, and the psychoses
An electroencephalogram (EEG) – The entire record of the brain wave– be used to diagnose and localize brain lesions, tumors, infarcts, infections,
abscesses, and epileptic lesions– A flat EEG (no electrical activity) is clinical evidence of death
The EEG be recorded with Scalp electrodes through the unopened skull or with electrodes on or in the brain.
A normal EEG
EEG PatternsEEG Patterns
Alpha: low-amplitude, slow, synchronous waves indicating an “idling” brain– Recorded from
occipital, parietal and frontal regions.
Person is awake, relaxed, with eyes closed.
– 8-13 Hz– 20 ~100 V.
Beta: high-frequency but low amplitude waves seen in deep sleep or person’s attention is directed to some specific type of mental activity
–Strongest from parietal and frontal lobes
•Produced by visual stimuli and mental activity.
–14-30 Hz
–5-20 V
Alpha Block: Replacement of the alpha rhythm by an asynchronous, low-voltage beta rhythm when opening the eyes.
•Theta :more irregular than alpha waves
–Emitted from temporal and parietal lobes.
•Common in newborn and sleep in adult.
•Adult indicates severe emotional stress.
–4-7 Hz
–100-150 V.
•Delta: high-amplitude waves;
•Emitted from temporal and occipital lobes.
•Common during sleep and awake infant.
•In awake adult indicate brain damage.
–0.5-3 Hz
–20 – 200 V
SPONTANEOUS CORTICAL
ELECTRICAL POTENTIALS:
THE EEG
the electrical responses of the axon and the dendrites of a large cortical neuron.
2. Mechanism of EEG
Current flow to and from active synaptic knobs on the dendrites produces wave activity, while AP are transmitted along the axon.
Mechanism of EEGMechanism of EEG
Continuous graph of changing voltage fields at scalp surface resulting from ongoing synaptic activity in underlying cortex
Inputs from subcortical structures– Thalamus– Brainstem reticular formation
• EEG signals generated by cortex
• Currents in extracellular space generated by summation of EPSPs and IPSPs
3. EEG Records During Epileptic Seizure
Epilepsy is characterized by uncontrolled excessive activity of either a part or all of the central nervous system.
Grand mal epilepsy: characterized by extreme neuronal discharges in all areas of the brain, last from a few seconds to 3 to 4 minutes.
Petit mal epilepsy: Characterized by 3 to 30 seconds of unconsciousness or diminished consciousness during which the person has several twitch-like contractions of the muscle.
Psychomotor seizure often associated with temporal lobe disease and characterized by complex sensory, motor, and psychic symptoms such as impaired consciousness with amnesia, emotional outbursts, automatic behavior, and abnormal acts.
II Wakefulness and SleepII Wakefulness and Sleep
SleepSleep
Sleep is a behavior and an altered state of consciousness– Sleep is associated with an urge to lie down for several hours in
a quiet environment Few movement occur during sleep (eye movements)
– The nature of consciousness is changed during sleep We experience some dreaming during sleep We may recall very little of the mental activity that occurred during sleep
We spend about a third of our lives in sleep
Two Types of SleepTwo Types of Sleep
Non-rapid eye movement (NREM)
Rapid eye movement (REM)
Non-REM SleepNon-REM Sleep
Alpha, delta, theta activity are present in the EEG record– Stages 1 and 2: Alpha waves– Stages 3 and 4: delta activity (synchronized)
Termed slow-wave sleep (SWS)
Light, even respiration Muscle control is present (toss and turn) Dreaming (not vivid, rational)
– Difficult to rouse from stage 4 SWS (resting brain?)
Types and Stages Types and Stages of Sleep: NREMof Sleep: NREM
Stage 1 – – eyes are closed and
relaxation begins – the EEG shows alpha
waves – one can be easily aroused
Stage 2 – – EEG pattern is irregular
with sleep spindles and K complex (combination of delta and theta)
– arousal is more difficult
• Stage 3 –
• sleep deepens
• theta and delta waves appear
• vital signs decline
• dreaming is common
• Stage 4 –
• EEG pattern is dominated by delta waves
• skeletal muscles are relaxed
• arousal is difficult
REM SleepREM Sleep
Presence of beta activity (desynchronized EEG pattern) Physiological arousal threshold increases
Heart-rate quickens Breathing more irregular and rapid Brainwave activity resembles wakefulness Genital arousal
Loss of muscle tone (paralysis) Vivid, emotional dreams May be involved in memory consolidation
Sleep Sleep Stage Stage
Cycles Cycles
A typical sleep pattern alternates between REM and NREM sleepSWS precedes REM sleep
REM sleep lengthens over the night
Basic sleep cycle = 90 minutes
The suprachiasmatic and preoptic nuclei of the hypothalamus regulate the sleep cycle
Importance of SleepImportance of Sleep Sleep is necessary
– for survival – for our nervous systems to work properly
During the SWS– growth hormone secretion increase – important for
infants growth physical restorative process of adult
During REM– brain blood flow and protein synthesis increase– important for
mental development of infants long-term memory and mental restoration in adults
Daily sleep requirements decline with age
What Happens if We are What Happens if We are Deprived of Sleep?Deprived of Sleep?
Lack of alertness Fatigue Memory problems Irritability Depression Lack of motivation Accidents Fibro Myalgia
Tips for Getting a Good NightTips for Getting a Good Night’’s Sleeps Sleep
Avoid caffeine and alcohol after dinnerKeep a routineDon’t go to bed hungry or right after eatingExerciseStop smoking
Rules for Optimal SleepRules for Optimal Sleep
Get an adequate amount of sleep every night
Establish a regular sleep scheduleGet continuous sleepMake up for lost sleep
REM DreamingREM Dreaming NREM DreamingNREM Dreaming
“vivid and exciting”
~3 per night
Longer, more detailed
Fantasy world
“just thinking”
Shorter, less active
Midst of nowhere
Logical, realistic
Frightening dream episodes
Occur in the REM stages
Last about 20 minutes
Can be result of taking drugs that affect neurotransmitter action or from drug withdrawal
Severe cases can be treated with medication
–Diazepam ( 安定) (tranquilizer)
NightmaresNightmares
Brain Mechanisms of Wakefulness and SleepBrain Mechanisms of Wakefulness and Sleep
The Control of Wakefulness– Two cholinergic pathways originate in the medulla
Dorsal path: RF--> to medial thalamus --> cortex Ventral path: RF --> to lateral hypothalamus, basal ganglia, and the
forebrain
– Activity in locus coeruleus ( 蓝斑核) and raphe nuclei (中缝核团)
The Initiation and Control of NREM Sleep– First segment of sleep is NREM– Locus coeruleus and raphe nuclei reduce activity– Thalamus synchronizes cortical activity
Brain Mechanisms of Wakefulness and Brain Mechanisms of Wakefulness and Sleep Sleep (( cont.cont. ))
The Initiation and Control of REM Sleep– REM-on areas in pons– Locus coeruleus and raphe nuclei become silent
Reactivation of locus coeruleus and raphe nuclei leads to either wakefulness or another segment of NREM sleep
Key Structures Involved With Key Structures Involved With Wakefulness, NREM, and REMWakefulness, NREM, and REM
PGO Waves Accompany REM SleepPGO Waves Accompany REM Sleep
Pontine-geniculate-occipital (PGO) wave
A synchronized burst of electrical activity that originates in the pons and like a wave it activates the lateral geniculate nucleus
and then the occipital lobe, specifically in the visual cortex
PGO waves appear seconds before and during REM sleep.
The Biochemistry of Wakefulness and SleepThe Biochemistry of Wakefulness and Sleep
Acetylcholine: High during wakefulness and REM Histamine
– High during wakefulness– Lower during REM and NREM
Norepinephrine and Serotonin ( 5-HT ) – High during wakefulness– Lower during NREM– No activity during REM
Adenosine (腺苷)– Builds up during wakefulness– Gradually drops during sleep
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