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

intracellular recording extracellular

recording

skin and bones

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

Occurs mostly in the frontal

region.13-275-10

During the activation of the

CNS (replaces the alpha waves after opening the eyes in bright light).

beta

Occurs most intensely in the

occipital and parietal regions.

7-1320-100

In all normal, adult persons, when they are

relaxed, awake in a quiet, resting state, without

visual sensation (i.e. closed eyes)

alpha

DistributionFrequency( Hz)

Voltage (uV)AppearanceBrain waves

Brain waves characteristics

- in all regions

0.5-450-200

-It is normal in children (2-3

years)- In adults in deep sleep

delta

-in temporal and frontal

region

4-730-70

-It is normal in children (2-5

years)- In adult only during the first stages of sleep.

theta

DistributionFrequency( Hz)

Voltage (uV)AppearanceBrain waves

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

Time (hours)

Stage 1

Stage 2

Stage 3

Stage 4

Awake

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 trackingand 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 eyejumps 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