Most tasks test memory within the same day, however, most forgetting occurs after 24 h. Further, testing memory for simple words or objects does not mimic real-world memory experiences. We designed a memory task showing participants video clips of everyday kinds of experiences, including positive, negative, and neutral stimuli, and tested memory immediately and 24 h later. During the memory test, we included repeated and similar stimuli to tax both target recognition and lure discrimination ability. Participants' memory was worse after 24 h, especially the ability to discriminate similar stimuli. Emotional videos were better remembered when tested immediately, however, after 24 h we find gist versus detail trade-offs in emotional forgetting. We also applied this paradigm to a sample of cognitively normal older adults that also underwent amyloid and tau PET imaging. We found that older adults performed worse on the task compared to young adults. While both young and older adults showed similar patterns of forgetting of repeated emotional and neutral clips, older adults showed preserved neutral compared to emotional discrimination after 24 h. Further, lure discrimination performance correlated with medial temporal lobe tau in older adults with preclinical Alzheimer's disease. These results suggest factors such as time between encoding and retrieval, emotion, and similarity influence memory performance and should be considered when examining memory performance for an accurate picture of memory function and dysfunction.
Background: Depression is associated with general memory impairment as well as a negativity bias, where negative experiences are better remembered. One potential mechanism underlying the negativity bias in depression could be pattern separation, a hippocampal computation that processes similar experiences as unique using non-overlapping representations, enabling individuals to remember the negative details of an experience. Mnemonic discrimination tasks, which provide a behavioral correlate of hippocampal pattern separation, have found that individuals with depressive symptoms show impaired general memory but enhanced negative mnemonic discrimination accompanied by a shift in amygdala-hippocampal dynamics (e.g. increased amygdala and reduced hippocampal activity). Antidepressants are one of the first-line treatments for depression, which have been shown to reverse hippocampal volume reduction, increase neurogenesis, and impact both memory and mood in rodent models. However, the impact of antidepressants on hippocampal pattern separation has not yet been examined in humans. Furthermore, antidepressants have limited efficacy toward successfully reducing depressive symptoms. Methods: We investigated the impact of antidepressants on memory using an emotional mnemonic discrimination task, where we previously reported a negativity bias in depression selective to mnemonic discrimination. Results: We found that individuals who reported a greater improvement in their depressive symptoms after taking antidepressants (responders) showed a reduction in the negativity bias and an enhancement in neutral mnemonic discrimination compared to those with no improvement (non-responders). Discussion: These effects were specific to mnemonic discrimination and not standard memorymeasures, suggesting that effective antidepressants can selectively enhance mnemonic discrimination and reduce the negativity bias observed in depression.
Stressful experiences are unavoidable, yet tactics can be employed to mitigate their impact on our cognition and well-being. Individuals with depression show dysfunctional emotion regulation, general episodic memory deficits, and a negativity bias, where negative experiences are better remembered. Recent work suggests that the negativity bias in depression may be driven by enhanced mnemonic discrimination, which relies on hippocampal pattern separation – a computation that processes experiences with overlapping features as unique. Depressed individuals show enhanced negative and impaired neutral mnemonic discrimination. Hippocampal pattern separation provides a mechanistic account for memory dysfunction in depression. The current study aimed to investigate emotion regulation training as a novel approach toward modifying mood and memory dysfunction in depression. Healthy and depressed participants performed an emotional mnemonic discrimination task, in which half of the participants were trained to apply an emotion regulation strategy (psychological distancing) during encoding. Psychological distancing is an emotion regulation strategy where one takes an objective, distant perspective. All participants rated their negative affect in response to each image. During retrieval, participants were shown repeated images, brand new images, or similar but not identical images (lures), which are critical for taxing hippocampal pattern separation. We found that applying psychological distancing during encoding rescued memory dysfunction in depression, evidenced by reduced negative affect as well as a reduced negative and enhanced neutral mnemonic discrimination during retrieval. These results suggest that emotion regulation strategies provide an effective approach toward altering mood and memory in depression.
Retirement is a period of significant change, as older adults transition from a lifetime of work to unstructured leisure time. This sudden shift in activity may have drastic consequences on cognition and disease risk. Retirement has been associated with declines in memory beyond typical age-related memory decline and may continue to deteriorate steadily the longer older adults remain retired. Mnemonic discrimination tasks have been developed that provide a more sensitive measure of age-related memory decline compared to traditional memory tasks by taxing hippocampal pattern separation, or the process of reducing interference across similar experiences. While older adults are more susceptible to interference in memory, positive experiences tend to be better remembered. The socioemotional selectivity theory suggests that awareness of a limited remaining lifespan leads older adults to prioritize positive experiences to facilitate emotional well-being. Therefore, retired older adults may be more susceptible to the positivity effect in aging. Here, we utilized an emotional mnemonic discrimination task to examine how retirement influences emotional memory. We found that retired older adults show selective impairments for mnemonic discrimination relative to standard memory measures, and a larger positivity effect in memory compared to their age-matched working peers. However, subjective memory complaints, job stress, and depressive symptoms impacted these relationships depending on retirement status. These findings are in line with the socioemotional selectivity theory, in which retirement may be associated with a prioritization of positive experiences; however, it is unclear whether this effect is compensatory or perhaps an indicator of age-related memory dysfunction.
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