EEG. ▫. Definition: the recording of electrical brain activity by electrodes placed
on the scalp. ▫. There is a significant amount of brain electrical activity.
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
