CORTICAL FEEDBACK INCREASES VISUAL INFORMATION TRANSMITTED BY MONKEY PARVOCELLULAR LATERAL GENICULATE-NUCLEUS NEURONS

We studied the effect of cooling the striate cortex on parvocellular l ateral geniculate nucleus (PLGN) neurons in awake monkeys. Cooling the striate cortex produced both facilitation and inhibition of the respo nses of all neurons, depending on the stimulus presented. Cooling the striate cortex also altered the temporal distribution of spikes in the responses of PLGN neurons. Shannon's information measure revealed tha t cooling the striate cortex reduced the average stimulus-related info rmation transmitted by all PLGN neurons. The reduction in transmitted information was associated with both facilitation and inhibition of th e response. Cooling the striate cortex reduced the amount of informati on transmitted about all of the stimulus parameters tested: pattern, l uminance, spatial contrast, and sequential contrast. The effect of coo ling was nearly the same for codes based on the number of spikes in th e response as for codes based on their temporal distribution. The redu ction in transmitted information occurred because the differences amon g the responses to different stimuli (signal separation) were reduced, not because the variability of the responses to individual stimuli (n oise) was increased. We conclude that one function of corticogeniculat e feedback is to improve the ability of PLGN neurons to discriminate a mong stimuli by enhancing the differences among their responses.