Lightning artifact in the EEG.

Lightning is highly prevalent in South Florida. The artifact caused by lightning in EEG recordings is of variable duration and seen as abrupt deflection of pens, sometimes followed by sustained pen drift and slow recovery mimicking amplifier overload as caused by rapid unplugging and plugging of the equipment power cable from the wall outlet. Since this artifact was associated to hospital light flickering and was recorded independent of machine location and orientation, we believe it is secondary to extreme brief Mains voltage fluctuations, probably due to horizontal lightning electric field effects rather than radio or electromagnetic interference generated by lightning.