Temporal dynamics of depression, cognitive performance and sleep in older persons with depressive symptoms and cognitive impairments: a series of eight single-subject studies

Abstract

Objectives: To investigate the presence, nature and direction of the daily temporal association between depressive symptoms, cognitive performance and sleep in older individuals. Design, setting, participants: Single-subject study design in eight older adults with cognitive impairments and depressive symptoms. Measurements: For 63 consecutive days, depressive symptoms, working memory performance and night-time sleep duration were daily assessed with an electronic diary and actigraphy. The temporal associations of depressive symptoms, working memory and total sleep time were evaluated for each participant separately with time-series analysis (vector autoregressive modeling). Results: For seven out of eight participants we found a temporal association between depressive symptoms and/or sleep and/or working memory performance. More depressive symptoms were preceded by longer sleep duration in one person (r = 0.39; p < .001), by longer or shorter sleep duration than usual in one other person (B = 0.49; p < .001), by worse working memory in one person (B = −0.45; p = .007), and by better working memory performance in one other person (B = 0.35; p = .009). Worse working memory performance was preceded by longer sleep duration (r = −.35; p = .005) in one person, by shorter or longer sleep duration in three other persons (B = −0.76; p = .005, B = −0.61; p < .001; B = −0.34; p = .002), and by more depressive symptoms in one person (B = −0.25; p = .009). Conclusion: The presence, nature and direction of the temporal associations between depressive symptoms, cognitive performance and sleep differed between individuals. Knowledge of personal temporal associations may be valuable for the development of personalized intervention strategies in order to maintain their health, quality of life, functional outcomes and independence.

Day-to-day reciprocal associations between depressive symptoms, cognitive performance, and sleep and the single-subject design

“…In summary, the current study by Zuidersma et al (2021) is a valuable addition to the research, which clearly shows that the presence, nature, and direction of the associations between sleep, depressive symptoms, and cognitive performance differ from individual to individual. The study further provides an insight into the day-to-day variations in these associations.…”

“…The authors list some limitations to their study, including the use of the single-subject design, which does not allow one to generalize the findings, whereas generalizability is one of the main aims of science. On the other hand, the single-subject design may lead to the development of daily intervention strategies to maintain health, quality of life, functional outcomes, and independence (Zuidersma et al, 2021). This is the strength of the current study, and it should be applauded because the single-subject design is a crucial method and certainly should be recognized and encouraged to be used when appropriate.…”

“…Surprisingly, the short-term associations are rather underexplored, even though it is well known that depressive symptoms, cognitive performance, and sleep quality show high day-to-day variability (Meeusen, 2014;Kim et al, 2016). The study by Zuidersma et al (2021) in this issue of International Psychogeriatrics addresses this subject by exploring short-term temporal associations of depressive symptoms, cognitive performance, and sleep in eight older persons with both depression and cognitive impairment.…”

“…Whereas most previous studies on daily associations between depression, sleep, and cognitive performance focused on the group-averages analysis, Zuidersma et al (2021) take into account individual differences. In the current work, the use of the single-subject design, an approach that analyzes each individual separately, was motivated by the fact that the group averages rarely can be applicable to individual persons, thus, limiting the value of the group-level analysis in clinical settings.…”

“…In the current work, the use of the single-subject design, an approach that analyzes each individual separately, was motivated by the fact that the group averages rarely can be applicable to individual persons, thus, limiting the value of the group-level analysis in clinical settings. Therefore, Zuidersma et al (2021) evaluated sleep, depression severity, and working memory during 63 consecutive assessments for each participant.…”