Each year in the U.S., bipolar disorder affects about six million adults, and about 16 million adults experience at least one major depressive episode, according to the National Institute of Mental Health. This study is the largest to date that examined motor-activity patterns in people who represent the full range of mood-disorder subgroups--(Bipolar I (BPI), Bipolar II (BPII) and major depression (MDD)--in a non-clinical population sample. Its findings are thus are more likely to apply to the general community and to offer usable clues about biomarkers for mood disorders.
The authors continuously monitored subjects' physical activities over a two-week period, using wearable actigraph devices. They used time-dependent regression models to investigate activity intensity and stability across diagnostic groups.
They found that among Bipolar I (BPI) patients, activity intensity was lower across the second half of the day and more variable in the afternoon, compared to controls. BPII patients showed increased variability during the dark period, compared to controls. These findings confirm accumulating evidence that BPI may be a manifestation of a rhythm disturbance that is most prominent during the second half of the day. Patients' activity patterns when they are not experiencing acute episodes provide evidence that activity dysregulation may be a potential biomarker for bipolar disorder.