ABSTRACT
Ultimately the limit on short-term unmasking-based plasticity resulting from discrete peripheral denervation must be set by the underlying anatomy. In addition to the role of local inhibition in limiting the extent of receptive fields which is implied from short-term unmasking studies, there are a number of direct physiological manifestations of the action of inhibitory intemeurons in the somatosensory cortex. In consideration of a possible source of tonic peripheral activity that may provide a source of input to central inhibitory neurons, C-fibre activity has been blocked using the selective neurotoxin, capsaicin. With extracellular recording from primary somatosensory cortex of anaesthetized macaque monkeys it was found that many neurons within the ‘hand’ representation had secondary receptive fields on the lower part of the face. The increased density, seen with anterograde transport of biocytin, was interpreted as resulting from axonal sprouting of intrinsic excitatory neurons and the formation of new terminal branches.
