Pattern-induced negative occipital potentials (PINOP).

: We describe 24 subjects (16 female, 8 male; age range, 3 to 36 years [mean, 15.7]) who exhibited a hitherto inadequately described EEG response to visual scanning of geometric patterns. Like lambda waves (the normal physiologic response to visual scanning of pictures), the responses to pattern scanning were occipitally distributed and disappeared on eye closure. In contrast to lambda waves, they were surface negative, briefer in duration, and sharper in contour. To designate them, we have coined the term pattern-induced negative occipital potentials (PINOP). The prevalence of epilepsy was not significantly different among subjects with PINOP than among age- and sex-matched control subjects who did not have PINOP. None of the patients with PINOP exhibited paroxysmal epileptiform responses to intermittent photic stimulation or pattern activation. We conclude that PINOP represent an unusual benign physiologic phenomenon. The restricted distribution over the posterior head region and absence of associated, more widely distributed epileptiform responses during photic stimulation and pattern testing are clues to the diagnosis. We hypothesize that a differential area of activation in the occipital lobe during pattern viewing versus picture viewing and orientation of the activated areas to the scalp electrodes may account for the differences in the morphology of the wave forms observed during conventional EEG recording.