over a bandwidth of about 25–500 Hz.
Electroencephalography (EEG) instrumentation is
similar to EMG instrumentation in terms of involving the
placement of many surface electrodes on the patient's skin,
specifically, on scalp. While EMG acquires the signals from
muscles below the skin, EEG attempts to acquire signals on
the patient's scalp, generated by brain cells. Simultaneously,
EEG records the summed activity of tens of thousands to
millions of neurons. As the amplifiers became small enough
to integrate with the electrodes, EEG has become to have the
potential for long term use as a brain-computer interface,
because the electrodes can be kept on the scalp indefinitely.
The temporal and spatial resolutions and signal to noise ratios
of EEG have always lagged behind those of comparable
intracortical devices, but it has the advantage of not requiring surgery. High performance
differential amplifiers are used for amplification. Signals of interest are in the range of 10 µV to
100 µV, over the frequency range of 1–50 Hz. Similar to EMG amplifiers, EEG benefits from
the usage of integrated circuit. The chances of EEG is also mainly from the asymmetrical
placement of electrodes, which leads to increased noise or offset.
Galvanic skin response
Galvanic skin response is a measurement of the electrical
conductance of the skin, which is directly influenced by how
much the skin is moist. Since the sweat glands are controlled by
the sympathetic nervous system, the skin conductance is crucial
in measuring the psychological or physiological arousal. The
arousal and the eccrine sweat gland activity are clinically found
to have direct relation. High skin conductance due to sweating
can be used to predict that the subject is in a highly aroused
state, either psychologically or physiologically, or both.
Galvanic skin response can be measured either as resistance,
called skin resistance activity (SRA) or skin conductance activity (SCA), which is a reciprocal of
SRA. Both SRA and SCA include two types of responses: the average level and the short-term
phasic response. Most modern instruments measure
conductance, although they both can be displayed with the
conversion made in circuitry or software.
cumulative activity of hundreds to thousands of neurons with
a sheet of electrodes placed directly on the surface of the
brain. In addition to requiring surgery and having low
resolution, the ECoG device is wired, meaning the scalp
Components of Medical Instrumentation System