Electrocorticography of waves associated with eye movements in man during wakefulness

Waves associated with horizontal saccadic eye movements were recorded from cortical occipital areas through multilead intracerebral electrodes implanted for a few days in 6 drug-resistant epileptic patients in order to localize epileptogenic foci. The waves were studied statistically when the EEG activity was not disturbed by interictal discharges. Cortical occipital waves related to free eye movements while scanning complex material started at the end of the eye movement, later in fact than the corresponding scalp parieto-occipital phenomena. The amplitude of the cortical waves increased with the complexity of the external field (contrasts having no marked effect) and was reduced in an unpatterned field and in dim light. Waves persisted in darkness. Their amplitude was independent of the size of the eye movement. The latency of the waves, calculated from the onset of eye movement, increased with the size of the movement, the complexity of the external field and also in darkness. Imposed eye movements induced cortical waves of larger amplitude and shorter latency and anticipatory potential changes beginning before onset of the eye movement. Waves related to eye movements differed from blinks and from responses to several types of light stimulation more strikingly in cortical records than in those from the scalp. These findings are discussed in relation to lambda waves, activation waves and eye movement potentials, expectancy waves and premotor potentials, and to the phenomena of perceptual blanks preceding normal perception after fixation of gaze. The importance of the subject's attention is emphasized.