Abnormal Sympathetic Lateralization in Depression: Asymmetry of the Biological Clock?

The suprachiasmatic nuclei (SCN), a paired structure in the hypothalamus controls the circadian rhythms of sleep-wake, endocrine, motor activity, and autonomic nervous system in mammals. Major depression, a common mood disorder, shows abnormal circadian cycles, however, the chronobiologic mechanisms involved are still unknown. Previous studies in animals show that the right/left SCN controls the ipsilateral sympathetic activity. To have an appreciation of the sympathetic activity in right-handed humans, we measured the electrodermal activity (EDA) in both wrists in five healthy and five major depression subjects. Healthy subjects showed higher right side activity compared to left (R > L). Depressed patients, showed the contrary (R < L). These findings open the question of whether each half of the body’s sympathetic activity depends on the ipsilateral SCN in humans. Also, the question was raised if abnormal asymmetries between right and left SCN could underlie depression’s circadian disorders. This exploratory research allows introducing new approaches to mental and chronobiologic disorder’s study in living humans.