(2012) applied a related concept to areas that show overall increased epileptic activity, but less so than putative ‘ictal cores’ ( Schevon et al., 2012 Weiss et al., 2013, 2015). With respect to the latter, the concept of ‘penumbra’ areas-zones of relative quiescence-during seizures has been examined in various contexts (see Lytton et al., 1997 for a computational study and brief review in the context of primarily generalized seizures). Furthermore, controversy exists over what is happening at the level of individual neurons within the seizure focus ( Bower et al., 2012), and what occurs outside this area as a seizure spreads into other areas ( Schevon et al., 2012). At the level of individual neurons, it appears that not all seizure activity represents strictly hypersynchronous activity amongst individual neurons ( Truccolo et al., 2011), and the degree to which any neural activity may be synchronous can depend highly on the type of seizure ( Truccolo et al., 2014). In the last decade or so, work from many groups using a variety of techniques has expanded on this simple model. This textbook model is a satisfactory shorthand for the overall process of a seizure, but neglects noteworthy heterogeneity and important unknowns. The canonical view of a typical seizure is that it represents excessive or ‘hypersynchronous’ activity in a large group of neurons. These studies, however, have also fuelled additional questions about how seizures can be defined, characterized and ultimately brought under control.

First in animal models and now more recently in human patients, studies of individual neurons have described how neural activity changes as seizures start, spread and terminate. Beginning in the 1950s, researchers began to address the physiology gap with recordings in models of seizures, including recordings of neural activity in small numbers of individual neurons. This significant shortfall prevents us from developing new treatments for the one-third of patients with epilepsy who do not obtain substantial control of their seizures with maximal medical therapy. However, the basic physiology of what occurs during a seizure remains poorly understood. Seizures are commonly accepted to be events characterized by brief periods of abnormal neuronal firing. This scientific commentary refers to ‘Single unit action potentials in humans and the effect of seizure activity’ by Merricks et al.

Neurons firing in the brain