Associative Processes in Spinal Reflexes

Summary

Acute, paralyzed, spinal cats were used to examine extinction and retention parameters as well as the involvement of cutaneous afferent terminals in classical conditioning of a hindlimb flexor nerve response. The CS consisted of a train of pulses delivered to the superficial peroneal (sensory) nerve and the UCS was a 50 V shock delivered to the ankle skin of the same hind leg. Conditions was measured as an increase in the response amplitude of the deep peroneal (motor) nerve. First, the effects of presenting massed vs. distributed extinction trials were explored. Conditioned response amplitude decrements were found when 60 extinction trials were administered immediately after aquisition at a rate of one per minute (massed condition). These decrements were not apparent when one extinction trial was delivered every ten minutes (distributed condition). From this data it is apparent that the conditioned response increase does not fall off spontaneously over a two hour period. In the second experiment, significant differences were not found between groups of animals allowed 1/2, 1, 2, 3, or 4 hr. between acquisition and extinction trials. These results were interpreted to indicate that response amplitude increases noted during acquisition were not the product of simple sensitization. Finally, excitability changs involving cutaneous afferent terminals were studied using the antidromic invasion technique. No tonic or phasic excitability changes were found over the course of training. This finding indicates that presynaptic facilitation is not involved in response amplitude increases observed during classical conditioning of the cat hindlimb flexor nerve response.