Seizures, Sleep, and the Midnight Sun

The well-known bidirectional link between seizures and sleep may be most conspicuous in environments where the chief zeitgeber - sunlight - undergoes extreme but consistent changes over the course of a year. Routine circannual encounters with the midnight sun and midday darkness strategically position Earth's polar regions as natural laboratories to study this effect. We reviewed 2337 studies that related status epilepticus (SE), light exposure, and sleep in people in the Arctic or Antarctic. Status epilepticus represented the most extreme - and arguably incontrovertible - expression of seizure. After applying filters and exclusion criteria, 5 studies were included for SE and 36 for sleep. Status epilepticus was correlated with increasing daylength going into summer (ie, brighter sunlight vector) at high latitudes. Sunlight and chronotype demonstrated a linear relationship, with more sunlight going into summer (ie, brighter sunlight vector) advancing chronotype, less sunlight going into winter (ie, darker sunlight vector) delaying chronotype, and extreme cases becoming free-running in either vector direction. U-shaped relationships were also surmised, with increased sleep fragmentation and decreased sleep duration for both brighter and darker sunlight vectors. A parsimonious synthesis is that a brighter sunlight vector advances chronotype to shorten and fragment sleep, thereby triggering more SE and seizures. Although these data are derived from Earth's poles, they are not specific to polar regions; rather, they hold ramifications for everyone on planet Earth - 1 in 10 of whom will have a seizure in their lifetime.