Why do we use relative signals and not absolute signals with EEG? Most EEG machines use a system based upon differential amplifiers to enhance the signal, a basic differential amplifier has 2 inputs and one output. the device takes 2 signals and outputs the difference between them (see this video). In short, the output is the difference between 2 signals and the differential amplifier discards the rest of the signal. But I think that possibly the current way of recording EEG could be encouraging loss of data due to ONLY looking for difference within EEG signals instead of analytical evaluation of absolute signals?
Why do we use relative signals and not absolute signals with EEG? Have there been any attempts to use absolute signals?
EEG measures voltage. By definition, voltage is an electric potential difference. There is no meaning of an &quot;absolute&quot; voltage, it's always a difference.
Yes, people &quot;attempt&quot; to measure a voltage with only one contact all the time, it happens whenever there is a broken channel or a failure of a ground wire. The result is an amplification of whatever other environmental signals can be picked up, dominated by AC current (&quot;60/50-cycle noise&quot;), radio waves, and other electromagnetic interference. A good ground wire is necessary to measure the small signals from the brain; something like an &quot;Earth ground&quot; would not be anywhere near sufficient.
You can get more local measures of voltage using electrodes in close proximity and measuring the potential between them rather than each against some other &quot;ground&quot;. Usually these are depth electrodes in the brain.