Scale-Invariant Locomotor Activity Patterns in Children with SAD

Abstract

Seasonal Affective Disorder (SAD) is a recurring mood disorder with symptoms of fatigue and diminished energy. A prominent characteristic of patients with SAD is disturbance in circadian and hemi-circadian rhythms. The purpose of this study is to investigate whether there are alterations in fluctuations within shorter time scales. Locomotor activity has scale invariant characteristics within a range of minutes and previous studies found alterations in these parameters for psychiatric disorders. In this study, we investigated the scale-invariant features of actigraph recordings of children with SAD. Fourteen children with SAD (11.0±3.3 years) and 12 age matched healthy controls (11.6±3.7 years) were recruited for the study. Wavelet analysis was used to calculate the scaling exponent of daytime and night-time activities. Scaling exponents for periods with higher (maxima) and lower levels (minima) of activities were calculated separately. Children with SAD had larger scaling exponents compared to controls during daytime for periods with higher and lower activities (daytime maxima: p<0.01, minima p<0.05). This means that healthy controls have more abrupt activity bursts and dips while children with SAD have more sluggish transitions in their activity levels. These findings were consistent in night-time activities.