Electroencephalography. Electrooculography []

THE ELECTROENCEPHALOGRAM (EEG)
THE ELECTROOCULOGRAM (EOG)
EEG





Definition: the recording of electrical brain activity by
electrodes placed on the scalp.
There is a significant amount of brain electrical activity.
This is influenced by the persons physical and mental state.
Electrical activity occurs in the brain at all times. This
activity is the result of the hundreds of thousands of cells in
the brain being activated at the same time.
This activity can be recorded as waves of different
frequencies (duration of the wave) and voltages (amplitude
of the wave).
The character of the waves depends on the degree of
activity of the cerebral cortex.
Electrical activity types of neurons
PA – action potential
PPSE – excitatory postsynaptic
potential
PPSI – inhibitory postsynaptic
potential
Methods of recording electrical
activity of the brain
skin and bones
intracellular
recording
extracellular
recording
In normal subjects the raw EEG can be filtered for four
frequency bands: alpha, beta, theta and delta waves.
BETA
ALPHA
THETA
DELTA
Brain waves characteristics
Brain
waves
alpha
beta
Appearance
In all normal,
adult persons,
when they are
relaxed, awake in
a quiet, resting
state, without
visual sensation
(i.e. closed eyes)
During the
activation of the
CNS (replaces the
alpha waves after
opening the eyes
in bright light).
Voltage (uV)
20-100
5-10
Frequency
( Hz)
7-13
13-27
Distribution
Occurs most
intensely in the
occipital and
parietal regions.
Occurs mostly in
the frontal
region.
Brain waves characteristics
Brain waves
Appearance
theta
-It is normal in
children (2-5
years)
- In adult only
during the first
stages of sleep.
-It is normal in
children (2-3
years)
- In adults in
deep sleep
delta
Voltage (uV)
Frequency
( Hz)
Distribution
30-70
4-7
-in temporal
and frontal
region
50-200
0.5-4
- in all
regions
Uses of EEG

monitoring consciousness (and by this anesthesia)

diagnosis of epilepsy

the study of the sleep stages and types

diagnosis of brain death
Epilepsy
Sleep stages and types
Awake
Stage 1
Stage 2
Stage 3
Stage 4
Time (hours)
Sleep stages and types
Recording technique
-Electrodes are placed on the scalp. The scalp must be degreased with
alcohol.
-The connections with the electroencephalograph are made (with
electric wires)
-The recordings are made in a quiet room, in resting state, awake,
with and without visual sensations (closed eyes).
- Recording with activation-stimulation of the central nervous system
are made by: opening the eyes in bright light, intermittent light
stimulation, acoustic stimulation…
Practical work
Recording EEG
EOG
Background :

One of the most important functions our eyes can perform is to fix or lock
on a specific region in our field of vision. There are two primary
mechanism used to track objects in our visual field: voluntary tracking
and involuntary tracking. The voluntary fixation allows us to move our
eyes in any directions we wish, and involuntary fixation allows us to track
an object in our visual field once it has been found.

An example of a specific involuntary tracking occurs when we read a text.
Rather than a smooth tracking motion , reading usually involves saccadic
movements, or fixating on a series of points in rapid succession (the eye
jumps from point to point at a rate of about three jumps per second, and
the jumps are so small that it is imperceptible to the person reading).
Typically , the eye will spend about 10% of the time moving from fixation
point to fixation point, with the other 90% of the time fixating on
individual words. What is especially interesting about this type of eye
movement is that even though the eye is jumping from place to place, the
motion appears smooth to the reader, as the brain suppresses images
during the saccades.
The eye is a spherical battery with the cornea ( or lens) representing the
positive terminal and negative terminal is behind the eye.
We can measure eye
movement by placing
electrodes on either side
of the eye. Because
electrodes measure
electrical activity, when
the cornea is closer to a
given electrode, the
electrode records a
positive potential. When
the eye is looking
straight ahead, it is
about the same distance
from either electrode, so
the signal is essentially
zero.
Practical work- electrodes placement and
lead connections for EOG horizontal
Practical work - electrodes placement
and lead connections for EOG vertical