Sleep, oscillations, interictal discharges, and seizures in human focal epilepsy

Bidirectional interactions between sleep and epilepsy are known since antiquity, however only the introduction of the method of electroencephalography (EEG) in 1929 contributed to objectively investigate and further unravel these obvious clinical relationships. Despite the increasing evidence over the last century, certain aspects of epilepsy and sleep interactions are still incompletely or not well understood. This article discusses the influence of sleep on adult focal epilepsy as assessed objectively via EEG, and highlights new developments of the last decade regarding sleep microstructure and new markers of the epileptogenic zone such as high-frequency oscillations > 80 Hz. It further describes evidence obtained from invasive intracranial EEG, as this is a unique method to assess directly cortical activity of superficial and deep structures of the human brain. Important achievements of the last decade were to unravel how epileptic activity is modulated by sleep, underlining the role of sleep slow waves to enhance epileptic activity, to demonstrate that seizure types are differently affected by sleep, and to show that sleep may be useful to better identify the epileptogenic zone for epilepsy surgery in drug-resistant epilepsy.