Response cost and time-place discrimination by rats in maze tasks

Time-place discrimination has been shown reliably in several avian and inse ct species, but only occasionally in rats and fish. In the present experime nts, we explored the effects of response cost on time-place discrimination by rats. In the first experiment, we increased the cost of making a choice and the cost of recovering from a wrong choice in two types of maze, a radi al arm and a vertical maze. In the radial arm maze, we found only general p lace preference, whereas in the vertical maze, we obtained evidence of time -place discrimination. In the second experiment, we found that the proporti on of rats showing time-place discrimination increased with the height and, therefore, the response cost of the vertical maze. These results suggest t hat rats do not automatically store and/or retrieve the time and place of r eward events but that response cost is an important trigger for time-place discrimination.