Pedunculopontine tegmental nucleus lesions impair stimulus-reward learningin autoshaping and conditioned reinforcement paradigms

The role of the pedunculopontine tegmental nucleus (PPTg) in stimulus-rewar d learning was assessed by testing the effects of PPTg lesions on performan ce in visual autoshaping and conditioned reinforcement (CRf) paradigms. Rat s with PPTg lesions were unable to learn an association between a condition ed stimulus (CS) and a primary reward in either paradigm. In the autoshapin g experiment, PPTg-lesioned rats approached the CS+ and CS- with equal freq uency, and the latencies to respond to the two stimuli did not differ. PPTg lesions also disrupted discriminated approaches to an appetitive CS in the CW paradigm and completely abolished the acquisition of responding with CR f. These data are discussed in the context of a possible cognitive function of the PPTg, particularly in terms of lesion-induced disruptions of attent ional processes that are mediated by the thalamus.