Monocular and binocular neuronal activity in human visual cortex revealed by electrical brain activity mapping

In the present study, we investigated topographical differences between monocularly and binocularly evoked potential fields related to the retinal location and spatial frequency of grating stimuli. Electrical brain activity was recorded in 18 healthy adults using an array of 21 electrodes over the occipital areas. Vertical black-and-white grating patterns of different spatial frequencies were presented with central fixation or lateralized to the left or right hemiretina. Computation of global field power determined component latency. Topographic characteristics of the field distributions were examined at the individual component latency for each subject using statistical comparisons between experimental conditions. The strength of the potential fields was significantly larger with binocular stimuli, whereas no effects were observed when comparing component latencies. Pronounced differences occurred in the spatial distribution of electrical brain activity: with 2.5 cycles/deg, large, significant topographic differences between monocularly and binocularly evoked activity were obtained. The potential fields showed a more anterior and more lateralized component distribution with binocular than monocular stimuli. In addition, when the gratings were presented binocularly, significant topographic differences were observed when low and high spatial frequency stimuli were compared. Our results suggest that the relationship between the topography of evoked components and retinal stimulus location and spatial frequency is different for monocular and binocular stimuli, indicating that binocular information processing triggers different neuronal processes in the human visual cortex.