P300- like event related potential amplitude in rats is a correlate of conditioned reinforcement

We have developed a methodology for recording a robust P300 event related potential (ERP) in rats. In these experiments a contingency shaped model of the human “oddball’ paradigm was employed in which rats were shaped to press a lever for food reinforcement signaled by the click of the pellet dispenser. A target tone cued the insertion of the lever that retracted after 1­sec or immediately following a single reinforced response, while a non­target tone was randomly presented. Brain activity was recorded through stainless steel electrodes implanted 1mm below the skull. Here, we compared the amplitude of the P300 response to the click of the pellet dispenser to the amplitude of the P300 response to the target and non­target tones. We found that the amplitude to food click was significantly greater that the amplitude to the target tone that cued lever insertion. Since the food click is more proximal to the primary reinforcer than the lever tone, it is a stronger conditioned reinforcer than the lever tone that sets the occasion for the food click. Accordingly we suggest that the P300 in rats is a correlate of conditioned reinforcement

Deletion of the trpc4 gene and its role in simple and complex strategic learning

The TRPC4 ion channel is expressed extensively in corticolimbic and a subpopulation of midbrain dopamine neurons. While TRPC4 knockout (KO) rats exhibit reduced sociability and social exploration, little is known about the role of TRPC4 in motivation and learning. To identify a function for TRPC4 channels in learning processes  we tested TRPC4 KO and normal wild type (WT) rats. TRPC4 KO and WT rats exhibited no differences in Y-­maze learning or simple discrimination learning. Furthermore, on a more complex serial reversal shift task designed  to assess strategic learning where the reward and non-­reward cues were repeatedly reversed between training sessions both TRPC4 KO and WT rats   performed equally well. Finally, we found no   performance differences when using a conditional reversal shift task where a tone signals the reversal of reward and non-reward cues within sessions. These data suggest that although TRPC4 channels may play a role in social interaction/anxiety  they exert a minimal role in simple and complex strategic learning

The Development of the P300 event related potential in rats during the initial stages of shaping lever pressing

Several experiments in our laboratory have shown that P300 ERP amplitude in rats is a decremental function of conditioned stimulus proximity to primary reinforcement in behavioral chains. We have also demonstrated robust P300 ERPs to stimuli predicting the occurrence as well as the omission of expected reinforcers. These findings support the hypothesis that the P300 is a correlate of the brain’s response to recognizing a conditioned reinforcer. In all the experiments we have conducted, the P300 was measured well after the response was established. The present experiment investigated the growth of the P300 during the shaping of the response to food delivery magazine (click training) and subsequent lever pressing. During this training a target tone (5.5 KHz, 70 db SPL) predicted the click of the pellet delivery magazine while a random non-target tone (2.5 KHz, 70 db SPL) was presented on a 8:1 non-target to target ratio. Seven rats received this training across 12 training sessions that consisted of 60 target tone-click-food pairings and 480 non-target tones. The mean amplitude of the P300 ERP to the target tone increased significantly across the 12 days reaching 128 µV and 95 µV on Days 11 and 12 respectively. Latency of the peak amplitude was about 800 msec and did not change significantly across the training sessions. Since the P30 ERP amplitude increased gradually across the sessions, during the time that the target stimulus was acquiring conditioned reinforcing properties, these findings further support the working hypothesis that the P300 ERP is a correlate of the brains recognition of a conditioned reinforcing stimulus

"The Effects of methamphetamine and cocaine on rats' Y-Maze performance using directional vs. visual cues"

Ryan J. Brackney, Kyle Sounhein, Rachel Mejia and Anna Marie Dolezal are students at Drake University. William D. Klipec is Associate Professor of Psychology in the College of Arts and Sciences at Drake University.Two experiments in our laboratory have demonstrated that across a wide range of doses, amphetamine but not cocaine (COC) disrupts the discrimination performance of rats running toward the lighted arm of a Y-Maze. In these experiments we noticed that rats in the amphetamine group were repeatedly running in the same direction (e.g., always left) rather than toward the lighted arm. Since amphetamine increases stereotypic behavior we hypothesized that the disruption of performance in the amphetamine group was due to perseverative responding in one direction. To test this hypothesis rats were trained on a directional cue that would be compatible with perseverative responding. One group of rats (n=8) was trained to run to the right arm (R) for water reinforcement while a second group of rats (n=8) was trained to run to the left arm (L). After reaching a 90% correct stability criterion, the rats were tested with an ascending and descending series of either methamphetamine (0.56 to 2.0 mg/kg) or COC (3.0 to 20 mg/kg) counterbalanced across groups, with saline and no injection days interspersed. With the exception of the 20 mg/kg COC dose, neither METH nor COC produced a significant increase in errors for rats in the R Group. The L Group, showed a significant increase in errors for METH at 0.56, 1.0 and 2.0 mg/kg and COC at the 10 and 20 mg/kg doses. The results were surprising in that METH did not result in perseverative errors and that it selectively effected rats trained to run left. We are currently investigating the handedness of the rats to determine if that accounts for the selective effect on left trained rats.Drake University, College of Arts and Sciences, Department of Psychology

"The rat P300 ERP to signaled occurrence and omission of expected reinforcers following extended training"

Brooke Schneider, Ryan J. Brackney, Jennifer Schwabe and Bryce Young are students at Drake University. William D. Klipec is Associate Professor of Psychology in Department of Psychology at Drake.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.Drake University, College of Arts and Sciences, Department of Psychology