Characterization of the neuronal changes in the medial prefrontal cortex during jaw movement and eyeblink Pavlovian conditioning in the rabbit.

Medial prefrontal (mPFC) single-unit activity was assessed in defensive (eyeblink, EB) and appetitive (jaw movement, JM) Pavlovian conditioning in the rabbit. Concomitant heart rate (HR) changes were also assessed. In a first experiment robust JM conditioned responses (CRs) were observed to a tone-water (CS+) contingency but not to tone-alone (CS-), indicating discriminative JM conditioning. However, the CS-evoked accelerative HR response was not discriminative. Nevertheless, several single-unit discharge patterns were evoked by both tone-water and tone-alone, many of which were uniquely associated with either the CS+ or CS-. In a second experiment, Three separate stimuli, consisting of tone followed by periorbital shock (tone-shock), water (tone-water), and white noise not followed by shock or water, were presented in the same paradigm. Discrimination of conditioned JM, EB and HR changes were observed, i.e. each of these behavioral responses were uniquely associated with the relevant CS presentation. Conditioned bradycardia was evoked by tone-water during the first training session, which changed to tachycardia with further training. However, conditioned bradycardia was evoked by tone-shock throughout training. Different subpopulations of mPFC cells were activated by the tone-shock and tone-water contingencies, but a small group of cells were activated by both.