background An episodic memory deficit, which is the inability to place a past event in its appropriate spatio-temporal context, is a neuropsychological core deficit of major depressive disorder, going along with medial temporal dysfunction. If that dysfunction is causally related to depression, it should be detectable even if performance is normalized by compensatory operations during remission.
method To test this hypothesis and to avoid confounding effects of chronicity and medication, we investigated eighteen unmedicated patients in remission from their first depressive episode and matched controls. While undergoing fmri subjects were instructed to memorize items embedded in a context (for example, real-world photographs of landscapes dyed in different colours) and subsequently retrieve that item information as well as contextual information.
results and conclusion As expected, there was no significant difference in memory performance or in gross brain structure between patients and controls. Hence, differences in brain activity cannot easily be related to mere differences in performance or gross brain structure. Our fmri findings reveal medial temporal dysfunction during episodic (contextual) encoding, which appears compensated by prefrontal processes during both encoding and retrieval. Hence, a medial temporal dysfunction might indeed be related to the cause underlying depression and not to consequences of the disease.