Learning at the level of the spinal cord: the role of associative and nonassociative mechanisms

Abstract

The phenomenon of Pavlovian conditioning has long been used to study the underlying neural mechanisms of learning. Prior studies have shown that a CS (CS+) that has been paired with an aversive US elicits antinociception. A similar effect has been described, in spinal rats. The present experiments explore whether the conditioned antinociception observed in spinal rats reflects true associative learning or alpha conditioning (nonassociative learning). Experiment I showed that the CSs used in earlier studies induced some antinociception before training. Experiments 2 and 3 showed that this antinociception habituated after exposure to the CS alone and that the habituation lasted one hour. Experiment 4 showed that presenting the US slowed the development of habituation when the CS was paired with the US, but not when it was unpaired. Experiment 5 explored the effect of increasing the intertrial interval (ITI) between CS/US presentations. I found that increasing the ITI prevented habituation to the CS-. Experiment 6 showed that increasing the number of CS-US pairings caused rats to habituate, effectively eliminating the conditioned response. These results indicate that conditioned antinociception in spinal rats is due to nonassociative rather than associative mechanisms. Implications of these results for other paradigms are discussed.