Crowding and Litter Effects on Retention and Reversal Learning by Young Rats

Abstract

72 rats both male and female from litters of 4 or 11, placed 1, 2, or 4/cage until age 65 days, acquired a position response under food deprivation. After 24 hr. each rat relearned to the same criterion, which was followed immediately by reversal training. Males acquired the response sooner, but females and litters of four retained more than their counterparts. Males housed 1/cage were slower to reverse than males housed 4/cage. When each group was subdivided into rats that consumed the reward upon the first correct response occurrence (immediate eaters) and those which did not consume the reward immediately (delay eaters), delay eaters required more trials to acquisition criterion, were slower to respond, had higher savings scores, and took longer to reverse. These findings, coupled with significant correlations of lower savings scores with greater increases in latency from acquisition to re-learning, suggested that emotionality interfered with retention by males and litters of 11. Similarly, emotionality that accompanies isolation was assumed to increase among male rats, to retard reversal learning, because the task increased in difficulty.