Paradigm for Social Recognition in Mice for Distinguishing Short- and Long-Term Relationships.

Social memory is the ability to remember and recognize conspecifics. It is a fundamental aspect of mammalian behavior, with demonstrated survival advantages in highly sociable mammals such as mice and humans. Rodents, particularly mice, are an established animal model extensively used to study social memory and its underlying mechanisms. Most existing social memory paradigms primarily assess short-term social recognition, wherein the relationship duration and familiarity level between the subject and an agent is between 5-15 min. Therefore, existing paradigms and past studies do not capture social memories from long-term relationships and focus on the novelty vs. short-term familiarity dichotomy, leaving a large gap in our mechanistic understanding of social memories. To fill this gap, we designed a simple assay that captures mouse responses to varying levels of familiarity, placing complex social memory recall in an observable, quantifiable context. In the four cups paradigm, a subject mouse freely explores an arena containing four perforated cups placed in each corner. These cups house three agent mice of varying familiarity levels (social stimuli): a long-term familiar (cagemate; 1 month co-housing), a short-term familiar (10 min of prior exposure), a novel conspecific, and an empty cup as a control. CD-1 male mice show a preference for investigating the novel and long-term familiar mouse over investigating short-term familiar mice in this paradigm. This task demonstrates recognition of familiarity level and minimizes aggressive behaviors while still controlling for exposure history. This novel assay provides a platform for directly comparing the neural mechanisms of social memory across long-term, short-term, and novel individuals. The four cups paradigm serves as a novel measurement for long-term familiarity recognition that will complement existing short-term recognition assays.