DISTRIBUTED REPRESENTATION OF VIBRISSA MOVEMENT IN THE UPPER LAYERS OF SOMATOSENSORY CORTEX REVEALED WITH VOLTAGE-SENSITIVE DYES

We have identified large-scale patterns of electrical activity in cort ical circuits that occur in response to stimulation of peripheral rece ptors. Our focus was on primary (S1) vibrissal cortex of anesthetized rat, and we used optical techniques in conjunction with voltage-sensit ive dyes to measure depolarization of the upper layers of cortex. Disp lacement of one vibrissa produced a field of activity that extends ove r very many cortical columns in S1. There are multiple, focal maxima w ithin this field. A global maximum is located near the center of the f ield of activity, and, as determined electrically and histologically, this site maps to the cortical column appropriate for the deflected vi brissa. The amplitude of this component attains a steady-state value u nder continuous stimulation. Additional temporal characteristics are r evealed by the response to a single displacement; the signal was triph asic and began with a prompt depolarization that was followed by a tra nsient phase of inhibition and a final phase of long-lasting depolariz ation. The somatotopy of the other, satellite maxima in the field of a ctivity were established through the reconstruction of the fields of a ctivity produced by individual stimulation of other vibrissae. Local m axima for one vibrissa were seen to overlie the global maximum found f or stimulation of nearest- and next-nearest-neighbor vibrissae. In con trast to the amplitude of the global maxima, the amplitude associated with the local maxima was not maintained with either continuous or inf requent but repetitive stimulation. Finally, the field of activity ind uced by alternate deflection of two neighboring vibrissae was suppress ed in amplitude in comparison to the summed amplitudes of the signals elicited by deflection of each vibrissa alone. We suggest that these p atterns of activity are a manifestation of the dynamic interaction amo ng neighboring cortical columns. (C) 1996 Wiley-Liss, Inc.