EC8073 Medical Electronics - Hints for Slow Learner Nadar Saraswathi College of Engineering and Technology, Theni, Tamilnadu, India.

1. N.Mathavan || AP – ECE – NSCET
ELECTROENCEPHALOGRAPHY [EEG]
EEG is the study of electrical activity of the brain. The biological name of brain is
Encephalon. Activity of brain is measured from electrodes that are placed on scalp.
1. Brain Major Parts
 Cerebrum
 Cerebellum
 Medulla oblongata
 Spinal Cord
2. Significance of EEG
3. Action Potential of the brain
 Inhibitory Post Synaptic Potential (IPSP)
 Excitatory Post Synaptic Potential (IPSP)
4. Evoked Potential
5. EEG Electrodes
6. Placement of Electrode
 Anterior – Posterior (Front – Back)Measurement
o Front Pole (FP)
o Frontal (F)
o Central (C)
o Parietal (P)
o Occipital (O)
 Lateral Measurements (21 Electrode Systems)
o Temporal Point (T)
o Central Point (C)
7. EEG Recording Method
 Unipolar
 Average Mode (Wilson Mode)
 Bipolar Mode
8. EEG Recording Setup
 Eight Channel Selector
 Differential Amplifier
 Signal Processing Unit
 Filter
9. EEG Waveform
 Alpha Wave (α Wave)
 Beta Wave (β Wave)
 Theta Wave (θ Wave)
 Delta Wave (δ Wave)

2. N.Mathavan || AP – ECE – NSCET
Brain Major Parts
 Cerebrum
It is responsible for the integration of complex sensory and neural functions and the
initiation and coordination of voluntary activity in the body.
 Cerebellum
It plays a vital role in the ability of the human being to maintain their balance
 Medulla oblongata
It is associated with the control of the functions like breathing, heart rate,
kidney function etc.,
 Spinal Cord
The large group of nerves that runs through the center of the spine and carries messages
between the brain and the rest of the body.
Significance of EEG
EEG is useful in the diagnosis of neurological disorders and sleep disorders. EEG is
primarily used for diagnosis including the following
 Helps to detect and localize cerebral brain lesions
 Aid in studying epilepsy
 Assist in diagnosing mental disorders
 Assist in studying sleep patterns
 Allow observation and analysis of brain responses to sensory stimuli
ACTION POTENTIAL OF TBE BRAIN
 Inhibitory Post Synaptic Potential
If the transmitter substance is inhibitory, then the membrane potential of the
receptor neuron increases in a negative direction. So that it is less likely to discharge. This
induced potential change is called as Inhibitory Post Synaptic Potential.
 Excitatory Post Synaptic Potential
If the transmitter substance is excitatory, then the receptor membrane potential will
increase in a positive direction. So that it is more likely to discharge and produces a spike
potential. This induced potential change is called as Excitatory Post Synaptic Potential.

3. N.Mathavan || AP – ECE – NSCET
EVOKED POTENTIAL
These are the potentials developed in the brain as the responses to external stimuli
like sound, light etc. It is also called as EVENT RELATED POTENTIAL.
EEG Electrodes
EEG electrodes transform ionic currents from cerebral tissue into electrical current
used in EEG preamplifier. 5 types of electrodes are used.
 Scalp: silver pads, discs or cups, stainless steel rods, chloride silver wires.
 Sphenoidal: Alternating insulated silver and bare wire and chloride tip
insertedthrough muscle tissue by a needle.
 Nasopharyngeal: Silver rod with silver ball at the tip inserted through the nostril.
 Electrocorticographic: Cotton wicks soaked in saline solution that rests on brain
surface.
 Intracerebral: sheaves of Teflon coated gold or platinum wires used to stimulate the
brain
Placement of Electrode
 Anterior – Posterior (Front – Back) Measurement
The distance between the Nasion and Inion over the head is divided into 5 points:
1. Frontal Pole (FP): 10% of Nasion
& Inion distance above Nasion.
2. Frontal (F): 20% of Nasion &
Inion distance from FP.
3. Central (C): 20% of Nasion &
Inion distance from F.
4. Parietal (P): 20% of Nasion &
Inion distance from C (Central Point).
5. Occipital (O): 10% of Nasion &
Inion distance from Inion.
Anterior - Posterior Measurement

4. N.Mathavan || AP – ECE – NSCET
 Lateral Measurements (21 Electrode Systems)
The Distance is measured from left to right point
Temporal Point (T): 10% of distance
from the pre-auricular point (from
one ear).
Central Point (C):20% of the same
distance.
EEG Recording Method
 Unipolar
Potential of each electrode can be measured with respect to one reference electrode.
 Average Mode (Wilson Mode)
Potential can be measured between one electrode & average of all other electrode.
 Bipolar Mode
Potential can be measured between successive pair of closely spaced electrode.
EEG Recording Setup
 Eight Channel Selector
The patient cable consists of 21 electrodes and is connected to the eight channel
selector. The electrodes are attached to the channel selector in groups of eight called a
montage of electrodes.
 Differential Amplifier
The 51 Hz interference is reduced by employing differential amplifiers as preamplifiers
with more than 81 dB CMRR and by use of 51 Hz notch filters. The effect of notch filter on
signal distortion is not so much because important EEG signals have frequencies below 31 Hz.
Lateral Measurement

5. N.Mathavan || AP – ECE – NSCET
 Filter
The output voltage from the amplifier may either be applied directly to the eight channel
display through the filter bank or it may be stored as data on a tape recorder or in a computer
memory for further processing. The filter bank consists of appropriate filters to select different
types of brain waves.
 Signal Processing Unit
Other facilities are also available to record evoked potentials from sensory parts of the
brain such that there are external stimuli like visual stimulus, audio stimulus and tactile
(touch) stimulus. The time delay between the stimulus and response can also be measured in
the signal-processing unit.
In the eight channel pen recorder there are 8 pens such that a pen for each channel. The
normal paper chart speed is 31 mm/second. There are also 61 mm/second for higher frequency
recording and 15 mm/second to conserve paper during setup time.
EEG Wavesform
The electrical recordings from the surface of the brain or from the outer surface of the
head demonstrate continuous electrical activity in the brain. The intensities of the brain waves
on the surface of the scalp range from 1-311uV and their frequencies range from 1.5 Hz to
111Hz.
Brain waves are irregular and no general pattern can be discerned in the EEG.
However at other times distinct patterns will appear

6. N.Mathavan || AP – ECE – NSCET
 Delta Waves(δ Wave)
Frequency : 1.5 to 4 HZ
Occurrence : These occur only once in every 2 or 3 seconds during deep sleep, in premature
babies and in very serious organic diseases. These can occur strictly in the cortex
independently by the activities in the lower regions of the brain.
 Theta Waves(θ Wave)
Frequency : 4 to 8 Hz
Occurrence : These are recorded from the parietal and temporal regions of the scalp of
children. These also occur during emotional stress in some adults particularly during
disappointment and frustration.
 Alpha Waves (α Wave)
Frequency : 8 to 13 Hz
Occurrence : They are found in normal persons when they are awake in a quiet resting
state. They normally occur in the occipital region. During sleep they disappear.
 Beta Waves(β Wave)
Frequency: 13 to 31 Hz
Occurrence: These are recorded from the parietal and frontal regions of scalp. These are
divided into two types as
 Beta I which inhibited by the cerebral activity and
 Beta II which excited by the mental activity like tension.