In a bipolar montage during EEG recording, what indicates a localizing sign?

In a bipolar montage during EEG recording, a phase reversal between adjacent channels that share a common electrode is a key indicator of a localizing sign. This phenomenon suggests that there is an underlying abnormality or focal activity in the brain area corresponding to the electrodes in question. Specifically, the phase reversal typically signifies that one region of the brain is exhibiting a different electrical activity compared to its neighboring area, which can help clinicians localize the source of any potential pathology.

This type of montage is particularly useful in visualizing how electrical activity propagates across the brain, allowing for the detection of localized discharges or seizures. The importance of phase reversal lies in its ability to provide clear evidence of changes in electrical activity that are not just generalized across the entire scalp but are concentrated in specific areas, making it a vital tool in neurophysiological assessment during surgical procedures.