Immediate thalamic sensory plasticity depends on corticothalamic feedback

Multiple neuron ensemble recordings were obtained simultaneously from both the primary somatosensory (SI) cortex and the ventroposterior medial thalam us (VPM) before and during the combined administration of reversible inacti vation of the SI cortex and a reversible subcutaneous block of peripheral t rigeminal nerve fibers. This procedure was performed to quantify the contri bution of descending corticofugal projections on (i) the normal organizatio n of thalamic somatosensory receptive fields and (ii) the thalamic somatose nsory plastic reorganization that immediately follows a peripheral deaffere ntation. Reversible inactivation of SI cortex resulted in immediate changes in receptive field properties throughout the VPM. Cortical inactivation al so significantly reduced but did not completely eliminate the occurrence of WM receptive field reorganization resulting from the reversible peripheral deafferentation. This result suggests that the thalamic plasticity that is seen immediately after a peripheral deafferentation is dependent upon both descending-corticofugal projections and ascending trigeminothalamic projec tions.