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