Light therapy as a treatment for epilepsy.

From a neurobiological level to epidemiological studies, there are four strands of evidence in the scientific literature that indicate that light therapy could be an effective treatment for some people with epilepsy. (1) Sunlight is important in the endogenous production and regulation of melatonin and vitamin D, both of which influence seizure thresholds. Although melatonin influences seizure thresholds, the relationship is complex. General down-regulating effects may have different effects on seizure thresholds for people with generalised and partial epilepsy syndromes. Specific actions within the hippocampus may mean that patients with temporal lobe epilepsy are particularly susceptible to the endogenous expression of melatonin via inhibitory actions on dopaminergic activity reducing seizure thresholds. (2) If suppression of melatonin results in fewer seizures this should be evident in seasonal variations in seizure frequencies. Seizure frequencies increase in the winter and on dull overcast days. Within this larger circannual rhythm, local light conditions are also associated with variations in seizure frequencies. Controlling for seasonal patterns, complex partial seizures are significantly less likely to occur on bright sunny days, than on dull days with fewer hours of sunshine, regardless of the time of year. (3) On a wider scale, some epidemiological studies also suggest a lower prevalence of epilepsy in southern Europe compared to Scandinavia and Northern Europe. (4) Light therapy is an established medical treatment for depression. Recent research suggests that some forms of epilepsy and depression are bi-directional conditions. The mechanism of action underlying light therapy for affective disorders remains the subject of much research but is thought to involve the enhancement of the monoaminergic systems targeted by antidepressant drugs (serotonin, dopamine, and norepinephrine); systems also implicated in a number of epilepsy syndromes. In this paper, we propose the hypothesis that exposure to high intensity light may be an effective, non-invasive add-on treatment for people with temporal lobe epilepsy. Although it is more likely to be palliative than curative, it may help smooth out some of the seasonal peaks in seizure frequencies, a pattern that increases the risk of serious manifestations of the condition such as status epilepticus and sudden unexpected death in epilepsy.