Health & Fitness

Instrumentation for Measuring Brain Function

joan croug

September 5, 2018

An electroencephalogram (EEG) is the representation of electrical activity of brain.
EEG is taken and the picked up signal is conditioned to make it suitable for recording and analysis.
Commonly used scalp electrode for EEG measurement consists of Ag-AgCl disks with long flexible leads that can be plugged in to the amplifier. Advantage of this type of scalp electrode is that they can accurately record even very slow changes in potential.
The most popular scheme used in the placement of electrode for the EEG pick up is the 10-20 electrode placement system.
Main regions of cranium are frontal, parietal, temporal and occipital regions. The electrodes placed in each region are denoted as F (Frontal), P (Parietal), T (Temporal) and O (Occipital).
In 10-20 electrode placement system we use 20 electrodes. One electrode is used for grounding the subject.
In 10-20 system, the nasion- inion distance is measured. Then points are marked on the shaved head at 10%, 20%, 20% and 10% of this length. Then the electrode is placed on these points. Hence this system is called 10-20 electrode system.
The EEG waveform differs in their shapes and they show dramatic changes to the different stages of sleep. Hence they are called EEG sleep patterns.
Montages are patterns of connections between the electrodes and the recording channels. The montage selection switch is used for selecting a particular channel.
The montage selector of an EEG machine is a large frame which consists of different switches so as to allow the user to select the desired electrode pair.
In an EEG machine, normally use high gain, high CARR operational amplifiers as preamplifiers due to its versatile features.
To filter out the noise contents, a bank of filters in the EEG machine system is selected according to the need.
The function of ADC is to convert the analog EEG signal to digital form. Thus the computer can store the EEG waveform for future reference.
The writing part of an EEG machine is usually consists of an ink type direct writing recorder. The recorder will be a chart paper which is driven by a synchronous motor.
The EEG signal is not useful for pin-pointing the exact source of activity. In, other words they are not very exact.
EEG waveform does not allow researchers to distinguish between activities originating in different but closely adjacent locations.
EEG measurements are functionally fast, relatively cheap and safe way of checking the functioning of different areas of brain.
The EEG neuro-feedback or EEG bio-feedback has many applications such as treating for physiological disorders and neurological disorders such as epilepsy.
Many disorders such as chronic anxiety, depression etc can be found out using as EEG pattern.
Hardware costs of EEG are lower when compared with other imaging techniques such as MRI scanning.
In EEG some voltage components can be detected even when the subject is not responding to stimuli.
EEG can be used in subjects that are not capable of making a motor response.