2. Electroencephalogram (EEG)
• is the record of electrical activity of the brain
• is recorded through the scalp
• EEG records may be bipolar or unipolar
• if the electrodes are placed on the surface of the cerebral
cortex, the record is called Electrocorticogram (ECoG)
3. Uses of EEG
• it is the best diagnostic tool available for assessing the
abnormalities of electrical activities of the brain
• it is a very helpful in diagnosing epilepsies & for
studying sleep & sleep disorders
4. • Physiological basis of EEG
• an EEG samples the summated activity of a very large
number of cortical neurons
• the record depends on the summation of excitatory &
inhibitory postsynaptic potentials
5.
6.
7.
8.
9. Features of EEG Rhythm
EEG
Rhythm
Frequency
(Hz)
Amplitude
(µV)
Associated features
Alpha
(α)
8-13 50-100 • found in normal adults when they are awake & in
a quiet, resting state
• occur most intensely in the occipital region but
can also be recorded from the parietal & frontal
regions of the scalp
Beta
(β)
13-30 5-10 • are recorded mainly from the parietal & frontal
regions during specific activation
Theta
(θ)
4-7 10 • occur normally in the parietal & temporal
regions in children, but they also occur during
emotional stress in some adults, particularly
during disappointment & frustration
• also occur in many brain disorders (degenerative
brain states)
Delta
(δ)
.5-4 20-200 • occur in very deep sleep, in infancy, & in serious
organic brain disease
10. Analysis of EEG
• The computer performs a Fast
Fourier transform analysis on 4s
segments of the EEG
• The smooth graphs form 4s
segments are packed
sequentially one down upon
another
• As a result of these operations,
the predominant frequency in
the EEG appears as a series of
tall peaks
11. • evoked potentials (or "evoked response")
• are the electrical responses to sensory stimulation
• clinically used EPs are
• brainstem auditory (BAEP)
• visual (VEP)
• somatosensory (SEP)
• are used mainly for
• assessment for clinically silent lesions in possible multiple
sclerosis
• visual loss that might be due to optic neuritis
• assessment of brainstem function in neonates
12. • Brainstem auditory evoked potential
• potentials recorded from the ear & the scalp in response to a
brief auditory stimulation
• assess conduction of the impulse through the auditory pathway
up to the midbrain
• Uses of BAEPs
• to assess hearing in uncooperative patients, & very young
children
• to detect degree of hearing loss in infants
• to assess the functions of the mid-part of brainstem
13. • Visual evoked potential
• potential recorded from the occipital region in response to
visual stimuli
• a normal cortical response is recorded when the entire visual
pathway is normal
• VEP can only detect the abnormalities, but cannot exactly
localize the site of the lesion in the visual pathway
14. • Somatosensory evoked potential
• potentials generated by large diameter fibers (sensory fibers)
in response to a sensory stimulus
• assess the intactness of the pathway for proprioception
15. • A seizure is a paroxysmal event due to abnormal excessive
or synchronous neuronal activity in the brain.
• Epilepsy can be defined as a condition in which seizures are
recurrent.
• Seizures may develop as a result of the spreading of EPSPs
• Seizure disorders may be idiopathic, but they also may
occur as a result of brain tumors & vascular malformations,
infections, drugs & metabolic problems
• can be classified into two major types:
1. Focal
2. Generalized
16. Focal seizures
• abnormality occurs in only one
part of the brain & the patients
does not lose consciousness
• focal epilepsy results from some
localized organic lesion or
functional abnormality, such as
• scar tissue in the brain that pulls on
the adjacent neuronal tissue
• a tumor that compresses an area of
the brain
• a destroyed area of brain tissue
• congenitally deranged local circuitry
17. • EEG in patients with focal seizures show sharp wave
18. Generalized seizures
• abnormality occurs in large areas
of the brain bilaterally, & patients
loses consciousness
• generalized seizures may result from cellular,
biochemical, or structural abnormalities that have a
more widespread distribution
19. Petit Mal Epilepsy
• is characterized by 3 to 30 seconds of unconsciousness
during which time the person has twitch-like
contractions of muscles usually in head region
• this is followed by return of consciousness &
resumption of previous activities
• the spike & rounded wave can be recorded over most or
all of the cerebral cortex
20. Grand Mal Epilepsy
• last from a few seconds to 3 to 4 minutes
• are characterized by loss of consciousness, tonic
phase, clonic phase
• the person remains in stupor for 1 to many minutes
after the seizure attack is over, & then often remains
severely fatigued & asleep for hours thereafter
• high-voltage, high-frequency discharges occur over the
entire cortex
21. • Sleep is defined behaviorally by four criteria:
• reduced motor activity
• decreased response to stimulation
• stereotypic postures
• relatively easy reversibility
• a person goes through stages of 2 types of sleep
• slow-wave (non-REM) sleep
• rapid eye movement (REM) sleep
• In a normal night of sleep, bouts of REM sleep lasting 5
to 30 min usually appear on the average every 90 min
22. Slow-Wave Sleep
• is exceedingly restful & is associated with decreases in
both peripheral vascular tone & many other vegetative
functions
• the dreams of slow-wave sleep are usually not
remembered because consolidation of the dreams in
memory does not occur
• Non-REM sleep is divided into four characteristic stages
23.
24. REM Sleep (Paradoxical Sleep, Desynchronized Sleep)
• is an active form of sleep usually associated with dreaming & active
bodily muscle movements
• person is even more difficult to arouse by sensory stimuli than during
deep slow-wave sleep
• muscle tone throughout the body is exceedingly depressed
• HR & RR usually become irregular
• irregular muscle movements do occur
• brain is highly active in REM sleep
• EEG shows a pattern of brain waves similar to those that occur during
wakefulness-paradoxical sleep
25. Basic Theories of Sleep
1. area for causing almost natural sleep is the raphe
nuclei in the lower half of the pons & in the medulla
• nerve fibers spread in the brain stem reticular formation &
into the thalamus, hypothalamus, limbic system, & the
neocortex of the cerebrum
• fibers extend downward into the spinal cord
2. stimulation of some areas in the nucleus of the tractus
solitarius can also cause sleep
3. stimulation of several regions in the diencephalon
(rostral part of the hypothalamus, the diffuse nuclei of
the thalamus) can also promote sleep
26. The Functions of Sleep
• Conservation of Metabolic Energy
• the metabolic rate during sleep is 15% less than during quiet
wakefulness
• Cognition
• humans show little or no physiological impairment after
several days of sleep deprivation but do show impaired
intellectual performance
• Thermoregulation
• body & brain temperatures are usually reduced during sleep
• Neural Maturation & Mental Health
• some reports indicate that REM sleep facilitates learning or
memory
