Regulation of the gain of visually guided smooth-pursuit eye movements by frontal cortex

In studies of the neural mechanisms giving rise to behaviour, changes in the neural and behavioural responses produced by a given stimulus have been widely reported. This `gain control' can boost the responses to sensory inputs that are particularly relevant(1-4), select among reflexes for execution by motoneurons(5,6) or emphasize specific movement targets(7). Gain control is also an integral part of the smooth-pursuit eye movement system(8-13). One signature of gain control is that a brief perturbation of a stationary target during fixation causes tiny eye movements, whereas the same perturbation of a moving target during the active state of accurate pursuit causes large responses(9). Here we show that electrical stimulation of the smooth-pursuit eye movement region in the arcuate sulcus of the frontal lobe (`the frontal pursuit area', FPA) mimics the active state of pursuit. Such stimulation enhances the response to a brief perturbation of target motion, regardless of the direction of motion. We postulate that the FPA sets the gain of pursuit, thereby participating in target selection for pursuit.