Seasonality, social zeitgebers and mood variability in entrainment of mood. Implications for seasonal affective disorder.

BACKGROUND

Seasonal variations in mood (seasonality) appear to be entrained to light, a physical zeitgeber. We hypothesised that people high in seasonality may be responsive to a range of zeitgebers, because of greater mood variability. We investigated whether the moods of people high in seasonality were more strongly entrained to the calendar week, a social zeitgeber, and whether any such effect was dependent on variability of mood.

METHODS

53 participants (14 male, 39 female; overall mean age=30) completed a daily mood report, over 56 consecutive days. Participants also completed the Seasonality Score Index (SSI) of the Seasonal Pattern Assessment Questionnaire. Each participant's time series of daily mood was analysed by spectral analysis to quantify the strength of their weekly mood cycle.

RESULTS

Participants with high SSI scores (> or =11) had significantly stronger weekly mood cycles than those with low SSI scores (<11), and significantly greater variability in mood. Covarying for mood variability reduced the difference between high and low SSI groups in mean strength of weekly mood cycle to non-significance.

LIMITATIONS

The time series of moods obtained was relatively short, and moods among high seasonal participants may have been affected by seasonal weather variability.

CONCLUSIONS

People high in seasonality appear to be more responsive to external zeitgebers, and this could be linked to their greater variability in mood. The integration of research on mood variability with research on SAD appears to be warranted.