Dependence of reward contingent positive variation (RCPV) and cortical synchronization on visual input in the cat

Cats trained to press a lever for milk reward display high amplitude low frequency electrocorticographic post-reinforcement synchronization (PRS) associated with epicortical steady potential shift, termed Reward Contingent Positive Variation (RCPV), over the parieto-occipital cortex. Previously, it was found that the PRS-RCPV phenomenon depends on unpatterned light input devoid of any conceivable information or conditional property. Although training in the dark most likely eliminated the "novelty" factor and the resulting orienting reaction to "light off" as a cause of PRS-RCPV suppression, a possibility could not be excluded that the absence of light had a negatively reinforcing property preventing the emergence of PRS-RCPV. Hence, in the present study an experimental paradigm was used in which "light off" and/or "tone on" cues signalled the availability of reward, the "light off" periods extending through the consummatory response. Seven out of 9 cats, despite 2-4 months of daily training, and 85% correct timing of bar press performance, never showed a PRS-RCPV response (one animal showed only sporadic and poorly developed patterns.) However, when the light was turned on during consumption, in 85% of such tests a fully developed PRS-RCPV emerged in a stimulus-bound manner. One animal was an exception and showed PRS-RCPV both in the absence and presence of light. It was concluded that light input plays a crucial role in the emergence of the PRS-RCPV phenomenon and therefore also participates in the integration of gustatory input.