A nerve cell in the primary somatosensory cortex of the brain responds to stimuli, such as touch, over a restricted part of the body surface. The peripheral area of stimulation that elicits activity in the cell is called the cell's "receptive field." When such a cell is deprived of its normal input, its receptive field shifts so the cell now responds to stimuli in areas that were ineffective earlier. These shifts may involve mechanisms similar to those the brain uses for other forms of plasticity, where change occurs during growth or during learning, by changing the effectiveness or presence of the connections called synapses among nerve cells. There are several levels of synaptic connections in the neural pathway from the skin to the cortex of the brain. This work uses electrophysiological recording, pharmacological agents to block specific kinds of normal synaptic activity, and local anesthetic to induce effects of temporary denervation in the cortex. These studies on single cells allow investigating the changes that occur over minutes rather than days, so the emphasis is on the fast mechanisms of neural signalling and transmission rather than the slow mechanism of new growth. In the novel approach here, not only the cortex will be studied, but also activity of subcortical single cells to define how shifts occur, and to determine the influence of cortical feedback connections on subcortical neurons. This integrative approach is likely to have impact beyond somatosensory work alone to the whole field of neural plasticity and the role of sensory experience to sensory and behavioral function.
