Recording and study of electrical activity of
Electrodes attached to the skull brain waves
can be recorded.
Brain waves are the sum of neuronal
depolarization in the brain due to stimuli
from 5 senses and the thought process.
Surface of brain voltage about 10mv
Due to propagation through skull
1 to 100 micro volts.
Frequency range 0.5 to 3000Hz.
These potential vary w r t to to position of
During recording electrodes are placed in
the FRONTAL. PERITAL , TEMPORAL
and OCIPITAL lobes of the brain.
EEG is the record of the brain waves made
by an electroenciphalograph
External stimulas ---. EVOKED
Measures the brain’s electric
activity from the scalp
Measured signal results from
the activity of billions of neurons
Amplitude: 0.001-0.01 mV
Bandwidth: 0.5-40 Hz
EEG Measurement set up
•10-20 Lead system is most
widely clinically accepted
•Brain research utilizes even 256 or 512
channel EEG hats
1. ALPHA WAVES
2. BETA WAVES
3. THETA WAVES
4. DELTA WAVES
Frequency 8- 13 Hz
Occurrence : Found in normal persons when
During sleep – disappear.
Amplitude – 20- 200 microvolts with a
mean of 50 Micro volt.
Frequency 13- 30 HZ
Occurrence: Perital and frontal lobes of the
They are two type
BETA- 1 inhibited by ceribral activity
B ETA-2 exited by the mental activity –
Frequency : 4- 8 HZ
Occurrence: Recorded from the perital and
temporal regions of scalp of children.
Also occurs during emotional stress.
Frequency : 0.5 – 4 HZ
Occurrence: Occurs only once in every two
or three seconds.
Deep sleep, in pre-mature babies and in
very series organic brain diseases.
ANALYSIS OF EEG
Helps physicians to diagnose
1. Level of consciousness
2. Sleep disorders
4. Brain tumors
REM means Rapid eye Movement
REM coinside with the period of dreaming.
EEG displays ch: features during
As anesthesia is applied brain wave
frequency decreases and amplitude
increases. Theta and delta wave appear.
Cerebral death – No signal
Brain tumor– No electrical signal originate.
A damped EEG is a sign of tumor
Epilepsy: Symptom for brain damage.
It may be due to defects in birth delivery,
Head injury during accident.
It may be due to brain tumor.