It is a curious feature of studies of recognition memory that the experimental subjects are almost always tested alone. They may be asked to scan a set of landscape pictures and later recognize having seen them before or to study a set of words or faces. For a social species such as ourselves—and mammals in general—being tested alone is a curious state of affairs. Social memory, social comparisons, and reciprocity have been a major driving force in brain evolution (1), and the effect of social interactions on memory deserves more attention. This experimental lacuna is now being put right, not only in social and evolutionary psychology and in work on “joint attention” by infants and their mothers, but also in animal studies that seek to identify the areas of the brain and the mechanisms mediating recognition of a familiar conspecific. On page 1536 of this issue, Okuyama et al. supplement behavioral analysis with an arsenal of modern viral vector–based, optogenetic, and imaging techniques to examine social memory (2). They identify the ventral hippocampus in the brain as critical for storing a social memory, or engram, with connectivity to the nucleus accumbens as key to the expression of such a memory (see the figure).
Authors: Kapil Saxena, Richard G. M. Morris