Plasticity in adult sensory cortex: a review

Abstract

There is growing evidence of significant plasticity in neuronal receptive fields and functional architecture in adult primary sensory cortex. Surgical lesions or rewiring of nerves in the periphery lead to large-scale changes in the corresponding cortical maps. Such changes are also seen after protracted training on sensory discrimination tasks, in a manner that reflects the subjects' improved discriminative abilities after training and is governed by their attentional state during training. More rapid and dynamic changes in cortical receptive field properties are seen with selective visual stimulation and during conditioning experiments. In the visual system, adult plasticity is clearly attributable to changes in cortex and not subcortical changes; moreover, the evidence suggests that the network of horizontal collaterals in primary visual cortex (V1) may play a significant role in V1 plasticity, both long-term and rapid. The same network is also likely to underlie some aspects of routine visual integration in V1. This leads to the speculation that plastic processes could form a part of routine cortical processing. At a cellular level, neurons in adult cortex possess the synaptic machinery that could underlie much of the observed adult plasticity. This includes short- as well as long-term activity-dependent processes for synaptic modification, as well as the modulation of such effects by the context of a task.