Study of Electrical Activity of Brain

1. VELTECH
DEPARTMENT OF ECE
Electroencephalogram- EEG
Prepared By,
V.Mahalakshmi,
Assistant Professor,
Department of ECE,
Veltech

3. What is EEG?
• Electroencephalography is the study of
electrical activity of the brain.
• The instrument used for measuring the
electrical activity of the brain is called
Electroencephalograph.
• The recording of the electrical activity of the
brain is called Electroencephalogram.
• The electrodes are placed on scalp.

4. Anatomy

5. Anatomy
• The brain is composed of the cerebrum,
cerebellum, and brainstem
• Cerebrum is the largest part of the brain and
is composed of right and left hemispheres.
• It performs higher functions like interpreting
touch, vision and hearing, as well as speech,
reasoning, emotions, learning, and fine
control of movement.

6. Anatomy
• Cerebellum is located under the cerebrum.
• Its function is to coordinate muscle movements,
maintain posture, and balance.
• Brainstem acts as a relay center connecting the
cerebrum and cerebellum to the spinal cord.
• It performs many automatic functions such as
breathing, heart rate, body temperature, wake
and sleep cycles, digestion, sneezing, coughing,
vomiting, and swallowing.

7. Anatomy
• The cerebral hemispheres have distinct fissures,
which divide the brain into lobes. Each
hemisphere has 4 lobes: frontal, temporal,
parietal, and occipital
Frontal lobe
• Personality, behavior, emotions, Judgment,
planning, problem solving
• Speech: speaking and writing ( Broca’s area)
• Body movement (motor strip)
• Intelligence, concentration, self-awareness

8. Anatomy
Parietal lobe
• Interprets language, words, Spatial and visual
perception
• Sense of touch, pain, temperature (sensory strip)
• Interprets signals from vision, hearing, motor,
sensory and memory
Occipital lobe
• Interprets vision (color, light, movement)
Temporal lobe
• Understanding language (Wernicke’s area)
• Memory, Sequencing and organization
• Hearing

9. ACTION POTENTIAL OF BRAIN
• The amplitude of the EEG is about 100 µV when
measured on the scalp, and about 1-2 mV when
measured on the surface of the brain.
• The bandwidth of this signal is from under 1 Hz to
about 50 Hz.
Evoked Potential:
• External stimuli such as light, sound etc. are
directed by sense organs, which cause some
changes in electrical activity of brain and some
potential is developed at this time which are
called evoked potential or event related
potential.

10. ACTION POTENTIAL OF 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 (IPSP).
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
(EPSP).

11. EEG LEAD SYSTEM
• The most popular scheme used in the placement of
electrode for the EEG pick up is the 10-20 electrode
placement system.
• The cranial area is divided into four main regions,
frontal, parietal, temporal and occipital regions.
• The electrodes placed in each region are denoted as
F (Frontal), P (Parietal), T (Temporal) and O
(Occipital).
• The 10-20 electrode placement system is
internationally used.
• In this set up the head is mapped by four standard
points. They are nasion, inion and left and right ears.

12. EEG LEAD SYSTEM

13. 10-20 EEG SYSTEM

14. 10-20 EEG SYSTEM
• Nasion and Inion are the two reference points near the ear lobes of the
human.
• Over the head, the distance between nasion and inion are divided into 5
points.
• The nasion – inion distance via the vertex is measured and three electrodes
are placed as 1 in frontal, 1 in central and 1 in parietal.
• They are placed at a distance of 10%, 20%, 20%, 20%, 20% and 10% of this
length.
• Now, similarly nasion – inion distance is measured along the temporal lobes
and five electrode are placed as two in frontal, 2 in temporal and 1 in
occipital lobes respectively.
• They are also placed at a distance of 10%, 20%, 20%, 20%, 20% and 10% of
this length on either side.
• Lastly, on the peripheries of the circle remaining six electrodes are fixed as 2
in frontal, 2 in central and 2 in parietal.
• So, in the setup totally 19 electrode are placed on the brain scalp and one
electrode which acts as reference is placed at the ear lobe.

15. EEG WAVEFORMS
• The brain waves are irregular.
• The intensity of the brain wave ranged from 0-
300µV.
• Frequency ranged upto 1/50sec.
• The EEG waveform is divided into
• Alpha Waves (α) 8-13 Hz
• Beta Waves (β) 14-30 Hz
• Theta Waves (θ) 4-7 Hz
• Delta Waves (δ) <3.5 Hz
• Gamma Waves (γ) 38-42 Hz or higher.

16. EEG WAVEFORMS
The Alpha Waves (α):
• Delta brainwaves are slow, loud brainwaves.
• It is recorded from occipital region of the brain.
• Its frequency range is 8-13 Hz.
• It can be measured from the normal person when
he is awake.
• Its amplitude is 20-200µV when the person is
sleeping, these waves are not appeared.
The Beta Waves (β):
• Its frequency range is 13-30 Hz.
• It is recorded from parietal and frontal regions of
the scalp.

17. EEG WAVEFORMS
The Theta Waves (θ):
• Its frequency range is 4-8Hz.
• It is recorded from parietal and temporal regions of the scalp.
• Usually this wave is measured from children.
• It can be measured from adults when are in emotional stress.
The Delta Waves (δ):
• Its frequency range is 0.5-4Hz.
• It is recorded from cortex of the brain.
• It is occurred in premature babies and when the person is in
deep sleep.
The Gamma Waves (γ):
• Gamma brainwaves are the fastest of brain waves (high
frequency, like a flute)
• Its frequency range is 38-42Hz.

18. EEG WAVEFORMS

19. EEG WAVEFORMS

20. EEG RECORDING SETUP

21. Applications of EEG
• Epilepsy diagnosis
• Anesthetic level
• Brain injury
• Monitoring during surgery.

22. • The patient cable consists of 21 electrodes and is connected
to the 8 channel selector. The electrodes are attached to the
channel selector in groups of 8 called a montage of
electrodes.
• The right ear electrode acts as reference electrode for the
right brain electrodes and left ear electrode act as reference
electrode for left brain electrodes.
• Output from 8-channel connector goes to the differential
amplifier bank. Differential amplifier is made of preamplifiers
that are used to reduce noise.
• The 50 Hz interference is reduced by employing differential
amplifiers as preamplifiers with more than 80 dB CMRR and
by use of 50 Hz notch filters.
• The effect of notch filter on signal distortion is not so much
because important EEG signals have frequencies below 30Hz.

23. • 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.
• This system helps to record the potentials generated from
the sensory parts of the brain. To achieve this, output unit
is connected with audio stimulus, visual stimulus and touch
stimulus.
• It can also measure the time delay between stimulus and
response from brain. In addition, we have a filter bank
consisting of low pass, high pass and band pass filters. They
help to remove noise from the brain waves.
• For the output recording, we can use either pen recorder or
CRO. Three modes namely Unipolar, Average mode and
bipolar recording are used to measure EEG.