By Tanya Gupta, 2021 Innovative Student Research Grant, Doctoral
Tanya’s graduate research has been centered around how animal behavior is entrained to different intervals of time in the seconds-to-minutes range, known as interval timing. Prior work has shown that the hippocampus (HPC), a brain structure critical for encoding memories, is also involved in interval timing, particularly when the timed intervals are long (>40s). However, evaluating this length-dependent effect in animal models is complicated by the observable link between timing behavior, motivation, and non-timing processes. Because timing tasks inherently impose a delay-to-reward, increasingly long intervals can induce schedule strain and reduce motivation to engage in the task, indexed by decreased frequency of trial initiation. Additionally, observed responses in timing tasks appear to be a mixture of timing and non-timing processes, and the proportion of non-timed behaviors has been shown to increase at longer intervals.
The SABA Innovative Student Research Grant will help fund the final study in Tanya’s doctoral dissertation, which will elucidate a specific role for the HPC in timing long intervals in rats, using a novel task which allows for simultaneous observation of timing behavior and other processes which may mediate HPC involvement. Rats in this study will be trained in a novel timing-with-opportunity-cost task, in which animals are trained to seek food at two levers. One of these levers (T) delivers reward after a fixed interval of time has elapsed. The other lever (P) delivers food with a low constant probability (e.g., 1/30 lever presses deliver food). On any given trial, rats are expected to respond primarily on the P lever, and increasingly “check” the T lever as the trained time of reinforcement gets closer. Following stable performance, animals will receive hippocampal infusions of muscimol, a drug which deactivates the target structure while it is onboard, and animals will be trained on a novel long interval. Then, Tanya will conduct analyses to assess the extent to which the HPC is needed to encode stable timed behavior, and whether any effect of interval length can be ascribed to changes in timing behavior or are related to other behavioral processes. This project is a culmination of Tanya’s previous work on the structure of behavior entrained to long intervals, and data collection is already underway.