"The rat P300 ERP to signaled occurrence and omission of expected reinforcers following extended training"
Klipec, William D.
Brackney, Ryan J.
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A series of experiments in our laboratory have shown that rat P300 ERP amplitude is an incremental function of conditioned stimulus proximity to primary reinforcement in simple behavioral chains, suggesting that the P300 is a correlate of the brain’s response to conditioned reinforcers. The present experiment was designed to investigate the P300 response to stimuli correlated with reinforcement (S+) and non-reinforcement (S-). A 500 msec 2.5 KHz non-target stimulus was presented on an 8:1 ratio with a 500 msec 3.5KHz stimulus that predicted the insertion of a lever. Lever responses on VR-6 reinforcement schedule produced a 500 msec tone with a frequency of either 4.5 or 5.5 KHz on a random 50% schedule. One tone predicted the delivery of a 45 mg food pellet while the other predicted the non-delivery of the pellet. S+ and S- tones were counterbalanced across rats. The P300 ERP to the S+ and S- tones were analyzed across 60 days of training. The results showed the development of a P300 ERP to both tones with the amplitude increasing across first the 12 days and maintained across the entire experiment. While the latency of the P300 to S+ was initially greater than the latency to S-, both latencies declined and converged across the first 12 days and did not differ significantly through the remainder of the experiment. These results demonstrate that the P300 ERP extends to the recognition of conditioned aversive stimuli as well as conditioned positive reinforcers. The similarity and stability of both S+ and S- P300 ERPs suggest that the P300 may be independent from reward affect and more related to the informativeness of the stimuli.
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