Binocularity in the lateral geniculate nucleus of the alert macaque

We examined the timing and the laminar distribution of binocular interactions and non-dominant eye effects in the lateral geniculate nucleus (LGN) of the alert macaque. Flash-evoked multiunit activity (MUA) was recorded simultaneously from multiple LGN laminae during contralateral eye, ipsilateral eye and binocular stimulation. Evidence of binocularity was noted in all laminae except 4. Inhibitory effects included (1) binocular suppression, a 15-70% reduction in the peak amplitude of MUA during binocular, compared to monocular stimulation of the dominant eye for that lamina, and (2) non-dominant suppression, a 10-45% reduction in MUA below its spontaneous level, with stimulation of the non-dominant eye. In lamina 3, the onset of this effect often preceded that of the excitatory response to stimulation of the dominant eye, and was coincident with non-dominant suppression in lamina 2, and with the dominant eye-mediated excitatory response in contralaterally innervated lamina 1. This is consistent with a parvo/magnocellular interaction. Corresponding excitatory effects, binocular and non-dominant facilitation, were also noted throughout LGN. The latter occurred both within the time frame of retinally driven activity (15-65 ms), and at longer latencies as well. The earliest response in lamina 6 of striate cortex, the origin of the corticogeniculate projections, was 30-35 ms, thus precluding a role of corticofugal modulation in the earlier effects in LGN.