Characterising longitudinal patterns in cognition, mood and activity in depression with high-frequency wearable assessment: an observational study (Preprint)

BACKGROUND Cognitive symptoms are an underrecognized aspect of depression that are often untreated. High-frequency cognitive assessment holds promise for improving disease and treatment monitoring. Although we have previously found it feasible to remotely assess cognition and mood in this capacity further work is needed to ascertain the optimal methodology to implement and synthesize these techniques. OBJECTIVE The objective of this study was to examine (1) longitudinal changes in mood, cognition, activity levels, and heart rate over 6 weeks; (2) diurnal and weekday-related changes; and (3) co-occurrence of fluctuations between mood, cognitive function, and activity. METHODS Thirty adults with current mild-moderate depression, stabilized on antidepressant monotherapy, responded to testing delivered via an Apple Watch for six weeks. Outcome measures included cognitive function using the Cognition Kit N-Back, assessing three brief n-back tasks daily; self-reported depressed mood assessed once daily; daily total step count and average heart rate. Change over a six-week duration, diurnal and day-of-week variations, and covariation between outcome measures were examined using nonlinear and multilevel models. RESULTS Participants showed initial improvement in the Cognition Kit N-Back performance followed by a learning plateau. Performance reached 90% of individual learning levels on average 10 days after study onset. N-back performance was typically better earlier and later in the day, and step counts were lower at the beginning and end of each week. Higher step counts overall were associated with faster n-back learning and increased daily step count was associated with better mood on the same (p<0.001) and following day (p = .02). Daily n-back performance covaried with self-reported mood after participants reached their learning plateau (p=0.01). CONCLUSIONS The current results support the feasibility and sensitivity of high-frequency cognitive assessments for disease and treatment monitoring in patients with depression. Methods to model the individual plateau in task learning can be used as a sensitive approach to better characterize changes in behaviour and improve clinical relevance of cognitive data. Wearable technology allows assessment of activity levels which may influence both cognition and mood.