Interval Timing and Motivation are Dissociable when Interval-Initiating Responses are Discriminable from Target Responses

Abstract

Data have accumulated suggesting that motivation and timing are correlated processes, yet few studies have tested whether motivation and timing are procedurally dissociable. This may be attributed to the fact that the most common framework in which to study timing, the pacemaker-accumulator model, does not readily suggest a route by which to dissociate motivation and timing. In contrast, the behavioral systems framework suggests that motivation and timing could be dissociated if subjects were trained in response-initiated (RI) interval-timing procedures rather than in common externally-initiated (EI) procedures. RI procedures were predicted to enhance temporal control and yield timing performance robust to fluctuations in motivation. Experiment 1 tested this hypothesis by training rats to either initiate switch-timing trials with a single press on the lever associated with the shorter FI schedule (SL-RI), or wait for switch-timing trials to be initiated (EI). Motivation was varied through pre-feeding. SL-RI and EI rats showed similar levels of temporal control and sensitivity to pre-feeding in their switch-timing performance. Experiment 2 tested a revised RI hypothesis, the discriminative-RI hypothesis, which predicts that as the trial-initiating response becomes progressively different from target responses, motivation and timing are increasingly dissociated. This experiment replicated Experiment 1 and added a trial-initiating condition in which a nose-poke into a nose port (NP-RI) initiated trials. As predicted, the sensitivity of switching-timing performance to pre-feeding scaled such that EI > SL-RI > NP-RI. These data suggest that it is possible to dissociate timing and motivation, challenging the notion that these processes are correlated.