SEASONAL AFFECTIVE-DISORDER - RESPONSE TO LIGHT AS MEASURED BY ELECTROENCEPHALOGRAM, MELATONIN SUPPRESSION, AND CEREBRAL BLOOD-FLOW

This study was designed to test the hypothesis that patients with SAD have significantly different physiological responses to light than hea lthy age- and sex-matched controls. We studied retinal contrast sensit ivity, visual evoked EEG responses, and melatonin suppression by, and cerebral blood flow response to, full-spectrum artificial daylight. Th ere was no significant difference between 10 patients and 11 controls in retinal contrast sensitivity, or amplitude or latency of N2, P2, P1 00 or P300 on EEG. We compared melatonin suppression in 12 SAD patient s and 12 controls. During exposure to 500 lux and 1500 lux artificial daylight both the SAD patients and controls had a significant melatoni n percentage suppression; however, the percentage suppression did not differ significantly between the SAD patients and the controls. In add ition, we carried out a small pilot study into the effect of light on cerebral blood flow in four SAD patients and four controls. Before exp osure to 1500 lux artificial daylight there was no significant differe nce between patients and controls in global, regional or cerebral hemi spheric blood flow. After light exposure the SAD patients and controls had a significantly different percentage change in cerebral blood flo w. We suggest that patients with SAD do not have significantly physiol ogical responses to light than controls, except perhaps in cerebral bl ood flow. Furthermore, mechanisms other than supersensitivity of melat onin suppression must explain both the pathophysiology of the disorder and its response to treatment with light.