EEG SMT CH1+ CH1- CH2+ CH2-

[ventolinmono]

Hi.
New in EEG.

In the EEG-SMT (Open EEG) What do the labels CH1+, CH1-, CH2+, CH2-, mean?
Are they four separate channels?
Why not label them CH1, CH2, CH3, and CH4?
Why the + and - signs?

Besides that I found in Wikipedia that DRL means: Driven Right Leg Circuit

A Driven Right Leg Circuit or "DRL" circuit is an electric circuit that is often added to biological signal amplifiers to reduce Common-mode interference. Biological signal amplifiers such as ECG (Electrocardiogram) EEG (Electroencephalogram) or EMG circuits measure very small electrical signals emitted by the body, often as small as several micro-volts (millionths of a volt). Unfortunately, the patient's body can also act as an antenna which picks up electromagnetic interference, especially 50/60 Hz noise from electrical power lines. This interference can obscure the biological signals, making them very hard to measure. Right Leg Driver circuitry is used to eliminate interference noise by actively canceling the interference.

- https://en.wikipedia.org/wiki/Driven_right_leg_circuit

[LubOlimex]

Hello there,

>>Are they four separate channels?

There are two channels only. Each channel consists of + and - electrode.

>>Why not label them CH1, CH2, CH3, and CH4?
>>Why the + and - signs?

It is because these are differential electrodes, so CH1 signal is the difference of (CH1+) and (CH1-).  The CH2 signal is (CH2+) - (CH2-).

The typical way to use the electrodes is to keep the CH1+ part of the channel attached on one of the brain's hemispheres (left or right) and the other part (e.g. CH1+) symmetrically placed on the other hemisphere.

Best regards,
Lub/OLIMEX