Light Therapy in Parkinson's Disease : Effect on Motor Symptoms, Sleep, Circadian Rhythms, and Mood

Parkinson's disease, a degenerative disorder of the dopaminergic system, combines motor symptoms but also non-motor, such as depression, sleep disorders and circadian rhythms and impaired cognitive functions. Difficulties in balancing the dopaminergic treatment of these patients emphasizes the need to find effective adjuvant therapies. Light therapy (LT) represents one such innovative therapeutic approach. Although light has an obvious to visual pathways within the brain, today it is known to additionally exert non-visual effects throughout the body. Recently our team has shown that non-visual, non-circadian light plays a major role in the regulation of sleep, as well as cognitive brain function in general. The retina, the primary conduit for the transmission of light information is weakened or thinned in Parkinson's patients. The dopamine system is known to enhance the processing of light information and intraocular injection of L-dopa in animal models of Parkinson's disease, can reverse associated motor symptoms. This allows for the possibility that LT would strengthen the dopaminergic tone in the central nervous system. However, to this date its effectiveness for alleviating Parkinson's symptoms has only been suggested by two studies, both poorly controlled. Thus, through the convergence of basic and clinical data, a study examining the effect of LT directly in people Parkinson's disease symptoms, whilst controlling for the effects on sleep, circadian system, mood, and cognitive functioning, is of extreme importance. With this information our hope is to determine if these polymorphisms allow for a predictive model of response to LT treatment.