[Ethological approach to seasonal depression and manic-depressive psychoses]

Some psychotherapists disagree with the importance of seasonal factors and sunlight in the etiology of depressions and bipolar disorders. Depression in spring and summer, mania in autumn and winter do not seem consistent with the expected effects of light on mood. Ethology offers an explanation: the variations of photoperiod can have opposite effects, depending on individuals, on territorial and hierarchical tendencies which constitute biological roots of mood disorders.