The Temporal Conditioning of Response Patterning in Mice
Delaney Fischer, Vassar College ’15 and Prof. Mark Cleaveland
In psychology a discriminative stimulus is an “environmental” input that informs the organism of the likely outcome of a behavior. For example, a green light tells a driver that pressing on the accelerator is acceptable, while in contrast a red light tells a driver that pressing on the accelerator can lead to an accident. In general, discriminative stimuli are thought of as exteroceptive -- that is, originating from outside the body. However, research has shown that internal stimuli, i.e., proprioceptive stimuli, can also condition behavior. An example of such a stimulus is the well-known circadian rhythm, which provides a temporal signal that informs behavior. In our experiment we explored another proprioceptive timing stimulus which has been termed “active time” (Cleaveland, 1999). Active time is defined as the time since the most immediate response. In this sense active time is a much more proximal signal than the circadian rhythm. We examined the role of active time in two different strains of mice using a discrete-trial procedure. Trials began with a lever press and the subsequent random drawing of a time interval (an interresponse time, or IRT) from a normal distribution ranging from 0.5 – 7.5 s. After the time interval had elapsed, subjects were given a choice of two levers, and switching/staying was reinforced depending upon the elapsed IRT. The experiment was counterbalanced such that for half of the subjects a “switch response” provided a higher chance of reward after a short IRT (0.5-3.0s), while a “stay response” provided a higher chance of reward after a long IRT (5.0-7.5s). The results of our study support and extend previous findings suggesting that active time can serve as a discriminative stimulus for response patterning. However, this suggestion only holds for one of our two strains of mice, raising questions about how genetic differences might relate to response patterning and/or timing.