It is well established that the responses of neurons in the
lateral geniculate nucleus (LGN) can be modulated by feedback
from visual cortex, but it is still unclear how cortico-geniculate
afferents regulate the flow of visual information to the cortex
in the primate. Here we report the effects, on the gain of LGN
neurons, of differentially stimulating the extraclassical receptive
field, with feedback from the striate cortex intact or inactivated
in the marmoset monkey, Callithrix jacchus. A horizontally
oriented grating of optimal size, spatial frequency, and temporal
frequency was presented to the classical receptive field. The
grating varied in contrast (range: 0–1) from trial to
trial, and was presented alone, or surrounded by a grating of
the same or orthogonal orientation, contained within either
a larger annular field, or flanks oriented either horizontally
or vertically. V1 was ablated to inactivate cortico-geniculate
feedback. The maximum firing rate of LGN neurons was greater
with V1 intact, but was reduced by visually stimulating beyond
the classical receptive field. Large horizontal or vertical
annular gratings were most effective in reducing the maximum
firing rate of LGN neurons. Magnocellular neurons were most
susceptible to this inhibition from beyond the classical receptive
field. Extraclassical inhibition was less effective with V1
ablated. We conclude that inhibition from beyond the classical
receptive field reduces the excitatory influence of V1 in the
LGN. The net balance between cortico-geniculate excitation and
inhibition from beyond the classical receptive field is one
mechanism by which signals relayed from the retina to V1 are
controlled.
Feedback from V1 and inhibition from beyond the classical
receptive field modulates the responses of neurons in the primate
lateral geniculate nucleus
