A comparison of responses and stimuli as time markers

Abstract

A rat's behavior, as well as a stimulus, may be a time marker. But do they lead to similar performance? Eight rats were trained on a 20-s DRL procedure in which head-entry responses were time markers, i.e., each head-entry response indicated that food would not be delivered for 20s. Concurrently, eight rats were trained on a control procedure in which light stimuli, yoked to the responses of a rat in the DRL procedure, were time markers, i.e., each light stimulus indicated that food would not be delivered for 20s. A comparison of performance between the two groups showed a lower response rate in the DRL procedure than in the yoked control procedure. However, similar response patterns between the two groups were observed, suggesting that rats anticipated the food similarly with a stimulus or a response as the time marker.

Figure 1

The yoked DRL-20 s procedure. For the Response Group (top line) a head entry was the best predictor of the time of food availability; for the Stimulus Group (bottom line) a 0.5-s light was the best predictor of the time of food availability. See text for details.

Figure 2

Upper panel: Responses per minute as a function of time from the last time marker averaged across the last 15 sessions of training. Lower panel: Normalized response rate as a function of time from the last time marker. For the Response Group, the last time marker refers to the last head entry, while for the Stimulus Group, it refers to the last light presentation.