We analyse a particular class of fast electrocortical rhythms that occur in a limited part of the primary visual cortex (BA 18) during eye saccades in behaving cats placed in a lit environment. Their high frequency (50-132 Hz) contrasts with that of two other classes of rhythms recorded in the same cortical area, the 25-45 Hz visual rhythms (40 Hz) that we previously showed to accompany sustained focused attention, and the alpha rhythms (approximately 10 Hz), that occur in situations of rest. These "very fast visual rhythms" (VFVRs) consist of two brief successive trains, a first one of low amplitude preceding the saccade onset, and a second one, much larger, during the saccade itself. The possibility is considered, that the first train subtends a presaccadic attention shift, and the second, a change of gaze towards a new target through the interception saccade. ECoG activities can thus well distinguish between attention shift and sustained attention.
