Slow Cortical Potentials (SCP’s) are very slow electrical shifts in brain activity. They change periodically from electrically negative to positive and play a significant role in the regulation of attention. A negative shift in the SCP signal represents activation of the cortex, increasing the firing probabilities of the underlying cortical areas. A positive shift represents an inhibition of the cortex and a decrease in firing probabilities. SCP’s are direct current (DC) shifts in the EEG and last from 300 msec to several seconds. The SCP itself does not have an absolute DC level, it is always a relative change from the starting point in the DC potential of the EEG.
SCP, how is it measured ?
SCP's are measured with en EEG electrode on the skin of the scalp. SCP can be measured with a true DC-amplifier. As the SCP signal is very vulnerable to artifacts, the SCP signal needs to be corrected for (in particular vertical) eye movements.
 | Brain Activity (EEG) |  | Eye Movement (EOG) |