Stress impairs spatial but not early stimulus–response learning

Recent evidence indicates that stress modulates multiple memory systems, favoring caudate nucleus-based stimulus–response learning at the expense of hippocampus-based spatial learning. Whether this is due to a facilitating effect of stress on stimulus–response learning, an impairing effect on spatial learning, or both, is not known. To answer this question, mice were either subjected to restraint stress, injected with vehicle or corticosterone or left untreated before training in two circular hole board tasks that could discriminate spatial and stimulus–response strategies. Stress, vehicle and corticosterone injection all impaired learning performance in the spatial task. Conversely, performance in the stimulus–response task was not affected by stress or corticosterone injection, although performance was generally lower than in the spatial task. Irrespective of the treatment, mice had to overcome the preference to use their spatial memory system to achieve the stimulus–response task. These findings suggest that (i) the caudate nucleus-based memory system is less stress sensitive than the hippocampus-based system and may thus dominate behavior in situations of stress and (ii) that multiple memory systems may compete for control of behavior even in tasks that can solely be solved by one system.