Electroencephalogram EEG, Wakefulness and Sleep

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Section 6 Electroencephalogram (EEG), Wakefulness
and Sleep
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Electroencephalogram (EEG)
1. Brain Waves
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Brain Waves State of the Brain

• Normal brain function involves continuous
  electrical activity
• Patterns of neuronal electrical activity recorded
  are called brain waves
• Brain waves change with age, sensory stimuli,
  brain disease, and the chemical state of the body
• An electroencephalogram (EEG) records this
  activity
• EEGs can 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

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The EEG be recorded with Scalp electrodes through
the unopened skull or with electrodes on or in
the brain.
A normal EEG
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Electroencephalogram (EEG)

• Measures synaptic potentials produced at cell
  bodies and dendrites.
• Create electrical currents.
• Used clinically diagnose epilepsy and brain
  death.

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EEG Patterns

• Alpha low-amplitude, slow, synchronous waves
  indicating an idling brain
• Recorded from parietal and occipital regions.
• Person is awake, relaxed, with eyes closed.
• 10-12 cycles/sec
• 50 100 ?V.

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• Betahigh-amplitude waves seen in deep sleep and
  when reticular activating system is damped
• Strongest from frontal lobes near precentral
  gyrus.
• Produced by visual stimuli and mental activity.
• Evoked activity.
• 13-25 cycles/sec.

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Alpha Block Replacement of the alpha rhythm by
an asynchronous, low-voltage beta rhythm when
opening the eyes.
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• Theta more irregular than alpha waves
• Emitted from temporal and occipital lobes.
• Common in newborn some sleep in adult.
• Adult indicates severe emotional stress.
• 5-8 cycles/sec.

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• Delta high-amplitude waves
• Common during sleep and awake infant.
• In awake adult indicate brain damage.
• 1-5 cycles/sec.

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SPONTANEOUS CORTICAL ELECTRICAL POTENTIALS THE
EEG
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2. Mechanism of EEG
Diagrammatic comparison of the electrical
responses of the axon and the dendrites of a
large cortical neuron.
Current flow to and from active synaptic knobs
on the dendrites produces wave activity, while AP
are transmitted along the axon.
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Mechanism of EEG

• EEG signals generated by cortex
• Currents in extracellular space generated by
  summation of EPSPs and IPSPs

• 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

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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.
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II Wakefulness and Sleep
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Sleep

• 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
• A basic issue is to understand the function of
  sleep

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EEG Sleep Patterns

• There are two major types of sleep
• Non-rapid eye movement (NREM)
• Rapid eye movement (REM)
• REM (rapid eye movement)
• Dreams occur.
• Low-amplitude, high-frequency oscillations.
• Similar to wakefulness (beta waves).
• Non-Rem (resting)
• High-amplitude, low-frequency waves (delta waves).

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Types of Sleep

• One passes through four stages of NREM during the
  first 30-45 minutes of sleep
• REM sleep occurs after the fourth NREM stage has
  been achieved

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Non-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 (could but not vivid, rational)
• Difficult to rouse from stage 4 SWS (resting
  brain?)

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Types and Stages of 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 (high-voltage wave bursts) arousal is
  more difficult

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• 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

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REM 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
• Pontine-Geniculate-Occipital (PGO) waves?
• Loss of muscle tone (paralysis)
• Vivid, emotional dreams
• May be involved in memory consolidation

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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 (first
relay of visual information) and then the
occipital lobe, specifically in the visual cortex
(which receives and puts together the visual
information that comes from the lat. geniculate
nucleus). PGO waves appear seconds before and
during REM sleep.
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Sleep Stage Cycles

• A typical sleep pattern alternates between REM
  and NREM sleep
• SWS 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

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Importance of Sleep

• Sleep is necessary for survival
• Sleep appears necessary for our nervous systems
  to work properly.
• During the SWS, growth hormone secretion increase
  and important for the infants growth and physical
  restorative process of adult
• During REM, brain blood flow and protein
  synthesis increase, and it is important for the
  mental development of infants and long-term
  memory and mental restoration in adults.
• Daily sleep requirements decline with age

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What Happens if We are Deprived of Sleep?

• Lack of alertness
• Fatigue
• Memory problems
• Irritability
• Depression
• Lack of motivation
• Accidents
• Fibro Myalgia

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Tips for Getting a Good Nights Sleep

• Avoid caffeine and alcohol after dinner
• Keep a routine
• Dont nap during the day
• Dont go to bed hungry or right after eating
• Exercise
• Stop smoking

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Rules for Optimal Sleep

• Get an adequate amount of sleep every night
• Establish a regular sleep schedule
• Get continuous sleep
• Make up for lost sleep

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Chemical Control of Sleep/Waking

• Sleep is regulated loss of SWS or REM sleep is
  made up somewhat on following nights
• Does the body produce a sleep-promoting chemical
  during wakefulness or a wakefulness-promoting
  chemical during sleep?
• Unlikely that sleep is controlled by blood-borne
  chemicals in the general circulation given
• Siamese twins share the same circulatory system,
  but sleep independently
• Bottle-nose dolphins the two hemispheres sleep
  independently

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Neural Regulation of Arousal

• Electrical stimulation of the brain stem induces
  arousal
• Dorsal path RF--gt to medial thalamus --gt cortex
• Ventral path RF --gt to lateral hypothalamus,
  basal ganglia, and the forebrain
• Neurotransmitters involved in arousal
• NE neurons in rat locus coeruleus (LC) show high
  activity during wakefulness, low activity during
  sleep (zero during REM sleep)
• LC neurons may play a role in vigilance
• Activation of ACh neurons produces behavioral
  activation and cortical desynchrony
• ACh agonists increase arousal, ACh antagonists
  decrease arousal
• 5-HT stimulation of the raphe nuclei induces
  arousal whereas 5-HT antagonists reduce cortical
  arousal

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Neural Control of SWS

• The ventrolateral preoptic area (VLPA) is
  important for the control of sleep
• Lesions of the preoptic area produce total
  insomnia, leading to death
• Electrical stimulation of the preoptic area
  induces signs of drowsiness in cats
• VLPA neurons promote sleep

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Neural Control of REM Sleep

• The pons is important for the control of REM
  sleep
• Pontine-Geniculate-Occipital (PGO) waves are the
  first predictor of REM sleep
• ACh neurons in the peribrachial pons modulate REM
  sleep
• Increased ACh increases REM sleep
• Peribrachial neurons fire at a high rate during
  REM sleep
• Peribrachial lesions reduce REM sleep
• Pontine ACh neurons project to the thalamus
  (control of cortical arousal), to the basal
  forebrain (arousal and desynchrony), and to the
  tectum (rapid eye movements)
• Pontine cells project via magnocellular cells
  within medulla to the spinal cord release
  glycine to inhibit alpha-motoneurons (induce REM
  motor paralysis or atonia)

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NT Interactions REM Sleep
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REM Dreaming
NREM Dreaming

• vivid and exciting
• 3 per night
• Longer, more detailed
• Fantasy world

• just thinking
• Shorter, less active
• Midst of nowhere
• Logical, realistic

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Nightmares

• 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 (tranquilizer)