Striate cortex increases contrast gain of macaque LGN neurons

Abstract

Recurrent projections comprise a universal feature of cerebral organization. Here, we show that the corticofugal projections from the striate cortex (VI) to the lateral geniculate nucleus (LGN) robustly and multiplicatively enhance the responses of parvocellular neurons, stimulated by gratings restricted to the classical receptive field and modulated in luminance, by over two-fold in a contrast-independent manner at all but the lowest contrasts. In the equiluminant plane, wherein stimuli are modulated in chromaticity with luminance held constant, such enhancement is strongly contrast dependent. These projections also robustly enhance the responses of magnocellular neurons but contrast independently only at high contrasts. Thus, these results have broad functional significance at both network and neuronal levels by providing the experimental basis and quantitative constraints for a wide range of models on recurrent projections and the control of contrast gain.

Corticogeniculate feedback sharpens the temporal precision and spatial resolution of visual signals in the ferret

“…Indeed, numerous studies using a variety of experimental techniques to manipulate CG feedback have documented changes in the magnitude of LGN responses (7)(8)(9)(10)(11)(12)(13)(14). Our results are consistent with some, but not all, of these observations.…”

“…Some have proposed that CG feedback modulates the gain (7)(8)(9)(10)(11)(12)(13)(14) and/or the spatiotemporal properties of LGN neurons (15)(16)(17). Others have proposed that corticothalamic feedback controls whether thalamic neurons are in a state of net excitation or inhibition (8,12), depending upon oscillatory activity in corticothalamic networks (18).…”

Feedback from V1 and inhibition from beyond the classical receptive field modulates the responses of neurons in the primate lateral geniculate nucleus

“…A mixed ANOVA revealed that extraclassical stimuli of either orientation were not any more effective in reducing the R max ratio in on-center cells (Ϫ0.27 6 0.04) than they were in off-center cells (0.23 60.04). Przybyszewski et al (2000) found that the gain of parvocellular and magnocellular neurons is increased by feedback from the striate cortex in the macaque. Unlike the stimulus paradigm used here, in their experiments they stimulated the classical receptive field but did not explore the effects of extraclassical stimuli.…”

“…We confirm this finding in magnocellular neurons in the marmoset, and extend it by showing results that suggest that the excitatory influence of the cortex in the LGN is blocked by stimulating beyond the classical receptive field. We used only stimuli that were modulated in luminance, and it may be that chromatic contrast is more effective for activating the feedback projection from V1 to parvocellular neurons (Przybyszewski et al, 2000). Parvocellular neurons were also less susceptible than magnocellular neurons to inhibition from beyond the classical receptive field.…”

“…A recent study in the macaque demonstrated that corticogeniculate afferents increased the gain of neurons in the LGN when the classical receptive field was stimulated (Przybyszewski et al, 2000). Gain control is certainly one mechanism by which corticogeniculate afferents could regulate the relay of visual information through the LGN to the cortex (Singer, 1977;Sherman & Koch, 1986;Koch, 1987).…”