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 con tribution of their principal components. Our experiments support the n otion that these components can be attributed to activation of two pyr amidal cell populations: supra- and infragranular. With well-habituate d stimuli EPs are dominated by a component related to the supragranula r cells (class 1). However, the first reinforcement of vibrissa stimul ation 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 (clas s 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 a ction elicited by contextual stimulation activates all neurons in the principal barrel column, including those providing an output to the su rrounding barrels. In the classical conditioning paradigm this mechani sm may lead to experience-dependent changes within the intracortical n etwork.