Locomotor micro-activities associated with therapeutic responses in patients with seasonal affective disorders

Psychomotor retardation, leaden paralysis and fatigue are often used to describe patients with depressive disorders. However, there is limited understanding of their meaning and how they are objectively manifested in the physical world. Patients with seasonal affective disorder (SAD) are characteristically hypoactive, and experience restoration in energy during effective treatment with bright light. In this study, we attempt to identify quantitative metrics of psychomotor activity that correspond to the clinical perceptions of hypoactivity and to the early activating effects of treatment.

Novel means of assessing the microstructure of activity was employed using wavelets and Hurst exponents to indicate the proclivity of subjects to persist at higher and lower levels of activity. This was assesed using actigraphs in 16 unmedicated patients with SAD before and following two weeks of bright light therapy.

Two weeks of phototherapy had no significant effect on mean levels of diurnal activity, but altered the microstructure of the activity. Specifically, phototherapy produced a significant reduction in inertial resistance in patients who had a 50% or greater reduction in Hamilton Depression scores (n=8), as reflected in reduced tendency to persist at low levels of activity. There was also a strong correlation between ratings of fatigue and measures of persistence at high versus low activity in initial responders, but not in initial non-responders.

These findings suggest that light therapy alters the nature of diurnal activity troughs in early responsive patients, reducing their tendency to persist at low levels, possibly reflecting an alleviation of psychomotor retardation.