Single-Neuron Correlates of Social Identity in Freely Interacting Female Rats

Abstract

The neuronal bases of social interaction are poorly understood, especially in terms of social motivation and social cognition. The present study used single-unit recording to investigate neuronal firing patterns in two inter-connected regions: the amygdala and the piriform cortex, focusing on the latter region. Olfactory signals strongly shape rodents’ social interaction: previous anatomical and physiological studies implicate the piriform cortex in olfactory pattern separation and pattern completion functions which could support memory for the odour profile of familiar conspecifics. As a first step in characterising the rodent social amygdala and piriform cortex, I paired Lister Hooded rats in an apparatus where they are fully free to engage in a variety of positive social interactions including anogenital sniffing, face to face contacts, and body contact. The apparatus was a 40x40 cm wooden square box with a wall height of 50 cm. I performed extracellular electrophysiological recordings from ensembles of single neurons tested in various social and non-social conditions (e.g. familiar rat in box vs empty box, or familiar rat vs novel rats). In addition, I simultaneously recorded behaviour with images time-stamped in synchronization with the electrophysiological recordings.
The present thesis shows that there are pyramidal neurons in the rodent amygdala and piriform cortex which respond strongly to social interaction. The main finding was that about 20% of cells in the piriform cortex showed firing patterns specific to either familiar or novel conspecifics, and a similar proportion showed firing patterns specific for one of two familiar sisters.