Probabilistic value learning in medial temporal lobe amnesia

A prevailing view in cognitive neuroscience suggests that different forms of learning are mediated by dissociable memory systems, with a mesolimbic (i.e., midbrain and basal ganglia) system supporting incremental trial-and-error reinforcement learning and a hippocampal-based system supporting episodic memory. Yet, growing evidence suggests that the hippocampus may also be important for trial-and-error learning, particularly value or reward-based learning. In the present report, we use a lesion-based neuropsychological approach to clarify hippocampal contributions to such learning. Six amnesic patients with medial temporal lobe damage and a group of healthy controls were administered a simple value-based learning task involving probabilistic trial-and-error acquisition of stimulus-response-outcome (reward or none) contingencies modeled after Li et al. (Proceedings of the National Academy of Sciences , 2011, 108 (1), 55-60). As predicted, patients were significantly impaired on the task, demonstrating reduced learning of the contingencies. Our results provide further supportive evidence that the hippocampus' role in cognition extends beyond episodic memory tasks and call for further refinement of theoretical models of hippocampal functioning.