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Abstract
The extensive distribution and simultaneous termination of seizures across cortical areas has led to the hypothesis that seizures are caused by large-scale coordinated networks spanning these areas. This view, however, is difficult to reconcile with most proposed mechanisms of seizure spread and termination, which operate on a cellular scale. We hypothesize that seizures evolve into self-organized structures wherein a small seizing territory projects high-intensity electrical signals over a broad cortical area. Here we investigate human seizures on both small and large electrophysiological scales. We show that the migrating edge of the seizing territory is the source of travelling waves of synaptic activity into adjacent cortical areas. As the seizure progresses, slow dynamics in induced activity from these waves indicate a weakening and eventual failure of their source. These observations support a parsimonious theory for how large-scale evolution and termination of seizures are driven from a small, migrating cortical area.
Highlights
The extensive distribution and simultaneous termination of seizures across cortical areas has led to the hypothesis that seizures are caused by large-scale coordinated networks spanning these areas
Recordings of clinical seizures were analysed in five patients implanted with microelectrode arrays (MEAs), as previously described[13,20,21]
The slowly propagating ictal wavefront is distinguished from travelling waves by its composition of steady firing lasting several seconds with minimal effect on low-frequency activity[13]
Summary
The extensive distribution and simultaneous termination of seizures across cortical areas has led to the hypothesis that seizures are caused by large-scale coordinated networks spanning these areas. Slow dynamics in induced activity from these waves indicate a weakening and eventual failure of their source These observations support a parsimonious theory for how large-scale evolution and termination of seizures are driven from a small, migrating cortical area. We proposed a spatiotemporal structure for seizures that corresponded with observations from both animal models[15,16,17] and spontaneous human seizures[13,18] In this structure, the seizing territory is led by a slowly advancing, sharply demarcated, narrow (o2 mm) band of continuous (tonic) multiunit firing, termed the ictal wavefront[13,19]. We hypothesize that gradual reduction in the excitatory currents generated from a slowly weakening ictal wavefront is sufficient to explain the evolution of both field potentials and multiunit activity (MUA) in the seizing territory, including the seizure’s eventual spontaneous termination
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