Cognitive processes that require spatial information rely on synaptic plasticity in the dorsal CA1 area (dCA1) of the hippocampus. Since the function of the hippocampus is impaired in aged individuals, it remains unknown how aged animals make spatial choices. Here, we used IntelliCage to study behavioural processes that support spatial choices of aged female mice living in a group. As a proxy of training-induced synaptic plasticity, we analysed the morphology of dendritic spines and expression of a synaptic scaffold protein, PSD-95. We observed that spatial choice training in young adult mice induced correlated shrinkage of dendritic spines and downregulation of PSD-95 in dCA1. Moreover, long-term depletion of PSD-95 by shRNA in dCA1 limited correct choices to a reward corner, while reward preference was intact. In contrast, old mice used behavioural strategies characterised by an increased tendency for perseverative visits and social interactions. This strategy resulted in a robust preference for the rewa...