MONOCULAR AND BINOCULAR NEURONAL-ACTIVITY IN HUMAN VISUAL-CORTEX REVEALED BY ELECTRICAL BRAIN ACTIVITY MAPPING

In the present study, we investigated topographical differences betwee n monocularly and binocularly evoked potential fields related to the r etinal location and spatial frequency of grating stimuli. Electrical b rain activity was recorded in 18 healthy adults using an array of 21 e lectrodes over the occipital areas. Vertical black-and-white grating p atterns of different spatial frequencies were presented with central f ixation or lateralized to the left or right hemiretina. Computation of global field power determined component latency. Topographic characte ristics of the field distributions were examined at the individual com ponent latency for each subject using statistical comparisons between experimental conditions. The strength of the potential fields was sign ificantly larger with binocular stimuli, whereas no effects were obser ved when comparing component latencies. Pronounced differences occurre d in the spatial distribution of electrical brain activity: with 2.5 c ycles/deg, large, significant topographic differences between monocula rly and binocularly evoked activity were obtained. The potential field s showed a more anterior and more lateralized component distribution w ith binocular than monocular stimuli. In addition, when the gratings w ere presented binocularly, significant topographic differences were ob served 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 dif ferent for monocular and binocular stimuli, indicating that binocular information processing triggers different neuronal processes in the hu man visual cortex.