CLASSICAL-CONDITIONING OF ELECTRICAL SELF-STIMULATION OF VENTRAL TEGMENTAL AREA TO BRIEF VISUAL-STIMULI IN RATS

Two groups of rats with bipolar electrodes implanted unilaterally into the left ventral tegmental area were trained to lever-press for the r esponse contingent electrical stimulation. After preliminary lever-pre ss training, two types of daily sessions were held on 10 consecutive d ays: type T+, current intensity set at the (T) under bar hreshold leve l and each response was accompanied by the visual signal (stimulus lig hts above the lever briefly went off); and type ST-, current set at th e (S) under bar ub (T) under bar hreshold level and no visual stimuli. On day 11, combination of the subthreshold current intensities and st imulus lights previously associated with the threshold stimulation (se ssion type ST+) resulted in a significantly elevated response rates co mpared to the performance under the subthreshold current without visua l stimuli (session type ST-). The extinction and recovery of this phen omenon are also demonstrated.