Cycles in epilepsy

In this Review, the authors provide an overview of the evidence for daily, multi-day and yearly cycles in epileptic brain activity. They also discuss advances in our understanding of the mechanisms underlying these cycles and the potential clinical applications of this knowledge. Epilepsy is among the most dynamic disorders in neurology. A canonical view holds that seizures, the characteristic sign of epilepsy, occur at random, but, for centuries, humans have looked for patterns of temporal organization in seizure occurrence. Observations that seizures are cyclical date back to antiquity, but recent technological advances have, for the first time, enabled cycles of seizure occurrence to be quantitatively characterized with direct brain recordings. Chronic recordings of brain activity in humans and in animals have yielded converging evidence for the existence of cycles of epileptic brain activity that operate over diverse timescales: daily (circadian), multi-day (multidien) and yearly (circannual). Here, we review this evidence, synthesizing data from historical observational studies, modern implanted devices, electronic seizure diaries and laboratory-based animal neurophysiology. We discuss advances in our understanding of the mechanistic underpinnings of these cycles and highlight the knowledge gaps that remain. The potential clinical applications of a knowledge of cycles in epilepsy, including seizure forecasting and chronotherapy, are discussed in the context of the emerging concept of seizure risk. In essence, this Review addresses the broad question of why seizures occur when they occur.

Automated summary

This Review provides an overview of the evidence for daily, multi-day, and yearly cycles in epileptic brain activity, discussing the potential clinical applications and highlighting technological advances. The authors address the question of why seizures occur when they occur, synthesizing historical, modern, and animal studies to uncover the mechanistic underpinnings of these cycles.