EEG WAVES AS DEFINED BY FREQUENCY:
ALPHA
Alpha waves are those between 7.5 and thirteen(13) waves per second (Hz).
Alpha is usually best seen in the posterior regions of the head on each
side, being higher in amplitude on the dominant side. It is brought out
by closing the eyes and by relaxation, and abolished by eye opening or
alerting by any mechanism (thinking, calculating). It is the major rhythm
seen in normal relaxed adults - it is present during most of life especially
beyond the thirteenth year when it dominates the resting tracing.
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DELTA
BETA
Beta activity is 'fast' activity. It has a frequency of 14 and greater
Hz. It is usually seen on both sides in symmetrical distribution and is
most evident frontally. It is accentuated by sedative-hypnotic drugs especially
the benzodiazepines and the barbiturates. It may be absent or reduced in
areas of cortical damage. It is generally regarded as a normal rhythm.
It is the dominant rhythm in patients who are alert or anxious or who have
their eyes open.
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DELTA
THETA
Theta activity has a frequency of 3.5 to 7.5 Hz and is classed as "slow"
activity. It is abnormal in awake adults but is perfectly normal in children
upto 13 years and in sleep. It can be seen as a focal disturbance in focal
subcortical lesions; it can be seen in generalized distribution in diffuse
in diffuse disorder or metabolic encephalopathy or deep midline disorders
or some instances of hydrocephalus
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DELTA
DELTA
Delta activity is 3 Hz or below. It tends to be the highest in amplitude
and the slowest waves. It is quite normal and is the dominant rhythm in
infants up to one year and in stages 3 and 4 of sleep. It may occur focally
with subcortical lesions and in general distribution with diffuse lesions,
metabolic encephalopathy hydrocephalus or deep midline lesions. It is usually
most prominent frontally in adults (e.g. FIRDA - Frontal Intermittent Rhythmic
Delta) and posteriorly in children e.g. OIRDA - Occipital Intermittent
Rhythmic Delta).
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DELTA
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