Fig. 4.

Possible circuitry to account for effects of S1 lesion on VPL RF size. (A) In the peripherally intact animal, corticothalamic input inhibits thalamic relay neurons by means of interneurons (IN) and reticular nucleus neurons (RT); cortical lesion produces RF expansion by removing this inhibition (Lower; gray lines indicate reduced activity). (B) At short intervals after amputation of D4, but after new inputs have started to appear from adjacent digits (D3), the thalamic GABAergic neurons are down-regulated (shaded circles) resulting in larger than normal RFs (Upper) and lack of an effect of cortical lesion (Lower). (C) At long intervals after amputation, GABA levels have recovered, leading to smaller, novel RFs (Upper) and expansion after cortical lesion (Lower).