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Episodic memories, when reactivated, can be modified or updated by new learning. Since such dynamic memory processes remain largely unexplored in psychiatric disorders, we examined the impact of depression on episodic memory updating. Unipolar and bipolar depression patients, and age/education matched controls, first learned a set of objects (List-1). Two days later, participants in all three groups were either reminded of the first learning session or not followed by the learning of a new set of objects (List-2). Forty-eight hours later, List-1 recall was impaired in unipolar and bipolar patients compared to control participants. Further, as expected, control participants who received a reminder spontaneously recalled items from List-2 during recall of List-1, indicative of an updated List-1 memory. Such spontaneous intrusions were also seen in the unipolar and bipolar patients that received the reminder, suggesting that memory updating was unaffected in these two patient groups despite impaired recall of List 1. Unexpectedly, we observed a trend towards higher intrusions, albeit statistically insignificant, not only in the reminder but also in the no-reminder subgroups of bipolar patients. We probed this further in a second cohort by testing recall of List-2, which was also impaired in both depression groups. Again bipolar patients showed intrusions, but this time in the reverse order from List-1 into List-2, independent of a reminder. Taken together, despite impaired recall, updating of episodic memories was intact and unidirectional in unipolar depression. In contrast, indiscriminate updating, as evidenced by bidirectional interference between episodic memories, was seen in bipolar depression. These findings reveal a novel distinction between unipolar versus bipolar depression using a reactivation-dependent memory updating paradigm.

ObjectivesTo explore the cognitive profile in urban Indian older adults and observe the prevalence of cognitive impairment associated with age, glycated hemoglobin (HbA1c) levels, vitamin B12, and other psychosocial factorsMethodsUrban community dwelling older adults (55-85years, n=123) underwent a detailed demographic and cognitive assessment comprising of tests from different cognitive domains – memory, executive function, visuospatial abilities, and verbal fluency. Serum samples were collected from a subset of participants (n=60) to determine HbA1c and vitamin B12 levels.ResultsPerformance in all cognitive domains declined with age. The decline became prominent around age 70. HbA1c correlated inversely with processing speed and executive function. Vitamin B12 did not correlate with performance on any cognitive test. Geriatric depression correlated inversely with visuospatial abilities. Surprisingly, stepwise multiple regression revealed that HbA1c and geriatric depression contributed to 28% variance on Montreal Cognitive Assessment whereas participant age did not contribute significantly. Mild Cognitive Impairment (MCI) was observed in 17% of participants. Participants classified as MCI had higher levels of HbA1c and geriatric depression, and lower performance in all cognitive domains compared to non-MCI participants.ConclusionAlthough cognitive performance declined with age, HbA1c and geriatric depression played a greater role than age in predicting cognitive decline. This study highlights the prevalence of metabolism linked changes in cognition in community dwelling Indian older adults.