title: Scalp spindles are associated with widespread intracranial activity with unexpectedly low synchrony.
abstract: In humans, the knowledge of intracranial correlates of spindles is mainly gathered from noninvasive neurophysiologic and functional imaging studies which provide an indirect estimate of neuronal intracranial activity. This potential limitation can be overcome by intracranial electroencephalography used in presurgical epilepsy evaluation. We investigated the intracranial correlates of scalp spindles using combined scalp and intracerebral depth electrodes covering the frontal, parietal and temporal neocortex, and the scalp and intracranial correlates of hippocampal and insula spindles in 35 pre-surgical epilepsy patients. Spindles in the scalp were accompanied by widespread cortical increases in sigma band energy (10-16 Hz): the highest percentages were observed in the frontoparietal lateral and mesial cortex, whereas in temporal lateral and mesial structures only a low or no simultaneous increase was present. This intracranial involvement during scalp spindles showed no consistent pattern, and exhibited unexpectedly low synchrony across brain regions. Hippocampal spindles were shorter and spatially restricted with a low synchrony even within the temporal lobe. Similar results were found for the insula. We suggest that the generation of spindles is under a high local cortical influence contributing to the concept of sleep as a local phenomenon and challenging the notion of spindles as widespread synchronous oscillations.
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, 3801 University Street, Montreal H3A 2B4, Canada; Innsbruck Medical University, Department of Neurology, Anichstrasse 35, A-6020 Innsbruck, Austria. Electronic address: birgit.frauscher@mcgill.ca.
authors.forename: Birgit
authors.initials: B
authors.lastname: Frauscher
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, 3801 University Street, Montreal H3A 2B4, Canada; CONICET-LEICI, Universidad Nacional de La Plata, Calle 1 y 47, La Plata B1900TAG, Argentina. Electronic address: nellen@ieee.org.
authors.forename: Nicolás
authors.initials: N
authors.lastname: von Ellenrieder
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, 3801 University Street, Montreal H3A 2B4, Canada. Electronic address: francois.dubeau@mcgill.ca.
authors.forename: François
authors.initials: F
authors.lastname: Dubeau
authors.affiliation: Montreal Neurological Institute and Hospital, McGill University, 3801 University Street, Montreal H3A 2B4, Canada. Electronic address: jean.gotman@mcgill.ca.
authors.forename: Jean
authors.initials: J
authors.lastname: Gotman
mesh_terms: D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D004567:Electrodes, Implanted; D004569:Electroencephalography; D006801:Humans; D012535:Scalp; D012815:Signal Processing, Computer-Assisted; D012894:Sleep Stages / Q000502:physiology*
keywords: Electroencephalography; Hippocampus; Human; Insula; Non-rapid eye movement sleep; Sleep physiology