Early and late acquisition of discriminative neuronal activity during differential conditioning in rabbits: Specificity within the laminae of cingulate cortex and the anteroventral thalamus.

Abstract

Multiple-unit activity of the cingulate cortex and the anteroventral (AV) nucleus of the thalamus was recorded during discriminative conditioning of an avoidance response (locomotion) in rabbits. A greater unit response was found in the cingulate cortex to the positive conditional stimulus (CS+; a tone paired with a footshock unconditional stimulus [UCS]) than the negative conditional stimulus (CS-; a tone randomly interspersed with the positive stimuli but never paired with the UCS). The majority of neuronal records obtained from the deep laminae (V and VI) of cingulate cortex manifested neuronal discrimination initially in the 1st exposure session to conditioning. The majority of neuronal records of the superficial laminae (I-IV) showed discrimination at a late stage of training, during the session in which the criterion of behavioral discrimination was met. The late developing discriminative activity of the superficial laminae was concident with the late developing discriminative activity of the AV thalamus. Once acquired, neuronal discrimination in cortex persisted throughout 600 ms after CS onset and during 6 sessions of training (overtraining) beyond criterion. The individual neuronal records suggested the persistance during overtraining resulted from replacement of early fading neuronal discriminations by late neuronal discriminations.