Distinct motor activity patterns for bipolar depression and mania

By Lucy Piper, Senior medwireNews Reporter

Acutely ill patients with bipolar disorder show distinct differences in motor activity regulation during episodes of mania and depression, research indicates.

Actigraphy findings showed that patients with bipolar depression had activity patterns characterised by high intra-individual variability, while those with bipolar mania had more complex patterns of activity.

Reduced 24-hour activity distinguished both groups of patients from mentally healthy controls, but not from each other.

“Our results provide strong indications that psychomotor function shows opposite symptom manifestations in acutely admitted patients with bipolar depression and mania,” say the researchers, led by Karoline Krane-Gartiser (Norwegian University of Science and Technology, Trondheim).

Actigraphy was conducted over a 24-hour period and during a 64-minute period of continuous activity in the morning.

Significant reductions in activity levels were seen for the 12 patients with bipolar depression, compared with the 28 mentally healthy controls, during the 24-hour period (128 vs 203 average counts/minute) and the active morning period (235 vs 391 average counts/min). The 18 patients with bipolar mania only differed significantly compared with controls during the active morning period (215 average counts/min).

Activity in patients with depression was defined by increased variability, as indicated by significantly increased standard deviation (SD) during the active morning period and root mean square successive difference (RMSSD) during the 24-hour and active morning period.

Both patient groups had a higher ratio of RMSSD to SD than controls. This reflects an increase in the alteration between successive activity counts relative to overall variability, the researchers explain in PLoS One. In patients with depression, this difference was significant during the 24-hour recording, whereas in those with mania the difference was significant during the 24-hour and the active morning period.

Corresponding with this, the patients with mania had a significantly lower first lag autocorrelation compared with controls in the active morning period, signalling less correlation between activity counts from minute to minute.

Although patients with mania showed less general variance in activity than patients with depression, Fourier analysis showed increased variance in the high frequency part of the spectrum, corresponding to the period from 2 to 8 minutes.

There was also evidence of increased complexity in the motor activity patterns of patients in the manic state, compared with the depressed state, who showed significantly more complexity in the symbolic dynamic analyses of the active morning period and increased sample entropy, indicating a higher level of disorder and unpredictability in a time series, says the team.

“It is possible that hospitalization in itself can explain the differences in activity between patients, as hospital programs and schedules may have increased activity for the patients with depression and restricted the patients with mania”, says the team.

“However, because the total 24-hour activity counts do not separate the patients with mania and depression, the differences found in other measures seem all the more significant, as they cannot be attributed to differences in total activity levels.”

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