Do rats run and respond at a higher rate to run during the dark phase when they are typically more active? To answer this question, Long Evans rats were exposed to a response-initiated variable interval 30-s schedule of wheel-running reinforcement during light and dark cycles. Wheel-running and local lever-pressing rates increased modestly during the dark phase. A second experiment examined the potential role of food-anticipatory activity in this effect by delaying postexperimental session feeding by 6 hr. No increase in wheel-running and lever-pressing rates was observed during the dark phase. This suggests that the effect of light/dark cycle on running and responding for the opportunity to run depended upon food anticipatory activity.
Belke, T. W.; Mandrona, A. R.; Conrad, K. M.; Poirier, K. F.; and Pickering, K. L.
"Effect of light/dark cycle on wheel running and responding reinforced by the opportunity to run depends on postsession feeding time,"
The Psychological Record: Vol. 58
, Article 4.
Available at: http://opensiuc.lib.siu.edu/tpr/vol58/iss3/4