Activation of the hippocampus is required to encode episodic memories for new events. Animal studies suggest that a release of dopamine generated by strong hippocampal activation is needed if these memories are to persist beyond 4 to 6 hours.
Based on these results, the authors of this paper tested the prediction that dopaminergic enhancement should improve human episodic memory persistence even for events encoded with weak hippocampal activation.
The effect of dopamine was studied in elderly human subjects in whom there is a loss of dopamine neurons as part of normal aging. Using pharmacological functional MRI, the dopamine precursor levodopa led to a dose-dependent (inverted U-shape) persistent episodic memory benefit for images of scenes when tested after 6 hours, independent of whether encoding-related hippocampal fMRI activity was weak or strong (U-shaped dose-response). The authors concluded that lasting improvement even for weakly encoded events supports a role for dopamine in human episodic memory consolidation. This has application for novel memory training strategies in the elderly human population.
Chowdhury R, Guitart-Masip M, Bunzeck N, Dolan RJ, Düzel E: Dopamine Modulates Episodic memory Persistence in Old Age. J. Neuroscience 32(41): 14193-14204 (2012).