Movement path as an ethological lens into interval timing

Interval timing behavior is traditionally investigated in operant chambers based on the very focal responses of the subjects (e.g., head entry to the magazine, lever press). These measures are blind to the movement trajectory of the animals and capture only a tiny segment and sometimes an idiosyncratic component of the animal's behavior. In other words, the state of the temporal expectancy is not observable at every time point in the trial. On the other hand, in nature, temporal expectancies guide actions in a much more complex fashion. For instance, an animal might approach a food patch at different degrees as a function of the expected time of food availability (e.g., nectar collection behavior). The current study aimed to investigate interval timing in a more naturalistic fashion by analyzing the movement trajectory of rats in fixed time (FT-30s) vs. variable time (VT-30s) schedules in modified open field equipment. We observed a temporally patterned movement in FT but not a VT schedule. In the FT schedule, rats moved away from the reward grid after consuming the presented water and were farthest from it at around 15 s, after which they started to approach the reward grid again. There was no such temporal patterning of movement trajectory in the VT schedule. Temporal control in the FT schedule was stronger when water was delivered close to the wall compared to when it was delivered close to the center of the open field. Our results show that movement trajectory may reflect instantaneous temporal expectancy.