Gating of the sensory activity within barrel cortex of the awake rat.

In rat barrel cortex, evoked potentials (EPs) to vibrissa stimulation can be divided into two distinct classes according to the relative contribution of their principal components. Our experiments support the notion that these components can be attributed to activation of two pyramidal cell populations: supra- and infragranular. With well-habituated stimuli EPs are dominated by a component related to the supragranular cells (class 1). However, the first reinforcement of vibrissa stimulation in the classical aversive paradigm favours the appearance of EPs dominated by a component characteristic of infragranular cells which matches with activation in the surround zone of the barrel field (class 2). Similar dynamic changes of the relative occurrence of the two EP classes follow other aversive stimuli, including pressing the animal's ear and restraining a whisker. We hypothesize that neuromodulatory action elicited by contextual stimulation activates all neurons in the principal barrel column, including those providing an output to the surrounding barrels. In the classical conditioning paradigm this mechanism may lead to experience-dependent changes within the intracortical network.