The onset, course and severity of bipolar disorder appear to be strongly modulated by regional light conditions and light-oriented behaviour. Seasonal variations in the incidence of depression, mania and suicidality have repeatedly been described. So far however, no sufficiently explanatory neurobiological model has been developed. The discovery of intrinsically photosensitive Retinal Ganglion Cells (ipRGC) containing the photopigment melanopsin, and their projections to many non-visual brain regions, has improved the understanding of the neuroanatomical links between light input, circadian rhythms, sleep, and mood.
Whereas the light therapy is well established as efficacious in seasonal affective disorder, the use of light therapy in bipolar depression remains more controversial.
Anna Wirz Justice will give a brief overview of circadian physiology and non-visual light effects, and summarise the evidence for the use of light therapy in bipolar depression. Michael Bauer will present new data on a large multinational sample (n=5536) of patients with bipolar-1 disorder linking age of onset and the incidence of suicide attempts to changes in regional light intensity (solar insolation). Exploring the potential neurophysiological mechanisms of non-visual light effects in patients, Philipp Ritter will present the results of two studies using narrow bandwidth blue light under laboratory conditions (n=90 & n=80) to evaluate melatonin suppression and phase shift in patients with bipolar-1 disorder. Finally, Francesco Benedetti will give a synopsis of chronotherapeutic combinations: light-therapy with antidepressant drugs, lithium or changes of the sleep wake cycle (sleep deprivation, sleep phase advance) for the treatment of depressive episodes and breakthrough suicidal ideation in bipolar disorder. His data suggest complex key mechanisms are involved in clinical response - rapid restoration of structural and functional cortico-limbic connectomics and synaptic homeostasis, together with monoaminergic potentiation and changes in glutamate neurotransmission.