Testing an increasing social working memory load in the female rat.

Across animal taxa, the ability to recognize members of one's species individually is a critical form of memory, mediating social interactions necessary for individual and species survival. A variety of laboratory behavioral tasks quantify conspecific social memory ability based on the premise of novelty exploration, in which the time spent exploring a novel, never-met conspecific is greater than the time spent exploring a familiar, previously-met animal. Here, we present a novel behavioral protocol that was designed for the systematic evaluation of social memory with an increasing memory load in the rat. This protocol considers and builds upon currently used behavioral tasks quantifying social memory between a load of two animals: one novel and one familiar. Two versions of the protocol were compared, one in which increases in memory load were progressive across trials (Progressive), and one in which the load challenge of each trial was semi-randomized (Nonprogressive). We found that young, gonadally-intact female rats demonstrated social memory of numerous conspecifics simultaneously. Specifically, rats could differentiate a novel conspecific from one, two, or three familiar conspecifics. At higher social working memory demands, in which there were more animals to remember and differentiate, social discrimination ability was absent. Additionally, the Progressive and Nonprogressive load conditions did not yield different patterns in social memory abilities. This social memory load task provides a relevant tool for the experimental evaluation of social memory in female rats, a memory type that is clinically relevant, conserved, and distinct from other memory types in neurobiological and neuroendocrine mechanisms.