Long-range interactions in the lateral geniculate nucleus of the New-World monkey, Callithrix jacchus

Visual stimulation of zones extending beyond the classical receptive field can modulate the contrast gain of neurons in the lateral geniculate nucleus (LGN) of cats, but little is known about the effect of extra-classical visual stimulation on the LGN of primates. Hence, we compare the effect of long-range interactions in parvocellular and magnocellular LGN layers of the marmoset monkey Callithrix jacchus using optimal, incremental spots flashed on the classical receptive field either alone or simultaneously with the shift of a grating (98% contrast; 0.1 cycles/deg) confined to a peripheral annulus (radii: 5-15 deg). The contrast required to drive the response halfway to saturation (c50) of most LGN neurons was raised by remote pattern shifts. The c50 ratio [(shift+spot)/spot] in OFF-center magnocellular neurons was significantly higher than in OFF-center parvocellular neurons. OFF-center magnocellular neurons closer to the fovea (<10 deg eccentricity) tended to have a higher c50 ratio than in more peripheral neurons. A significant drop in visual sensitivity to 25% contrast spots was observed during remote motion: d' fell from 1.8 to 1.4 in parvocellular neurons and from 2.2 to 1.7 in magnocellular neurons. Such long-range interactions produce a reduction in visual sensitivity by changing the gain of the geniculate relay and point to an inhibitory, motion-sensitive extra-classical receptive field in both parvocellular and magnocellular pathways, which may be involved in saccadic suppression and attentional mechanisms in early vision.