Performance of 11- and 14-day-old rats on a working memory problem

Abstract

Independent groups of 11- and 14-day-old Sprague—Dawley rat pups were trained on a patterned (single) alternation task at intertrial intervals (ITIs) of 8, 30, or 60 sec. In this runway task, animals encounter a regularly alternating schedule of rewarded and nonrewarded trials and learn to respond discriminatively on the basis of information from the previous trial (working memory). The 14-day-olds learned to alternate at the 8- and 30-sec but not the 60-sec ITI. The 11-day-olds learned to alternate only at the 8-sec ITI where they were nevertheless impaired relative to the 14-day-olds. Random partial-reinforcement control groups showed no evidence of alternation learning at any ITI. These data confirm earlier claims by this laboratory that infant alternation learning depends on intertrial memories and raise the possibility that the memorial and associative processes subserving patterned alternation learning are developing over the 11- to 14-day age range in the rat.