​​​​​FROM SNIFFING TO KNOWING WHO: CORTICAL AMYGDALA MANIFOLDS ENCODE CONSPECIFIC IDENTITY

Social odors convey conspecific identity and familiarity, but the population mechanism for individual recognition remains unclear. We recorded single-unit activity in the posteromedial cortical amygdala (PMCo) of female mice during repeated sampling of three urine stimuli (two unfamiliar males, self-urine). Although urine-selective responses were detectable at the single-unit level, strong inter-trial variability and widespread mixed selectivity motivated a population-manifold approach.
We reconstructed low-dimensional population trajectories for each stimulus and quantified how their geometry evolved with experience. Across trials, PMCo activity reorganized into stimulus-specific manifold subspaces that progressively differentiated the two unfamiliar individuals, indicating consolidation of an identity-specific population code through repeated sampling. This organization did not rely on dedicated “identity neurons”; instead, identity was expressed through distributed mixed-selective contributions and the emergent geometry of the population manifold. By contrast, self-urine induced minimal manifold reshaping, consistent with a highly familiar cue requiring little updating of the identity representation. Because individual urine signatures are shaped in part by major urinary protein (MUP) composition, these results suggest that exploration-driven manifold reorganization links molecular individuality in urine to an explicit neural identity representation.
Funding: PID2022-141733NB-I00 (MCIU/AEI/10.13039/501100011033/FEDER, UE); CIAICO/2023/041 (Conselleria d’Educació, Cultura i Universitats, Generalitat Valenciana).