title: Relationships between interictal epileptic spikes and ripples in surface EEG.
abstract: OBJECTIVE
  Ripples (80-250Hz) have been shown to be a more specific biomarker for the epileptogenic zone than epileptic spikes in intracranial EEG and even surface EEG. Ripples often co-occur with spikes. We investigated the spatiotemporal relation between spikes and ripples, and differences between spikes that do and do not co-occur with ripples.
  
  
  METHODS
  We marked 50 time points with spikes in bipolar surface EEG during NREM sleep in patients with focal or multifocal epilepsy. We marked ripples that occurred with spikes and calculated parameters relating spikes and ripples: the duration, amplitude and slope of spikes, the timing of the start of ripples and spikes and the proportion of overlap.
  
  
  RESULTS
  In total 219 ripples and 5995 individual spikes were marked in 31 patients. Spikes with ripples were on average shorter, had higher amplitude and higher slope than spikes without ripples. 64% of ripples started before spikes started. Spikes occurred on 13 (5-26) channels per patient, and ripples on 3 (0-14) channels, which were also spike channels.
  
  
  CONCLUSIONS
  Ripples precede rather than follow spikes, so ripples are unlikely to result from spikes.
  
  
  CONCLUSIONS
  Ripples and spikes seem not one-on-one coupled, but certain states of the brain can accommodate both.
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada; Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Center Utrecht, The Netherlands. Electronic address: n.vanklink-2@umcutrecht.nl.
authors.forename: Nicole
authors.initials: N
authors.lastname: van Klink
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Birgit
authors.initials: B
authors.lastname: Frauscher
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Center Utrecht, The Netherlands; SEIN - Stichting Epilepsie Instellingen Nederland, Heemstede, The Netherlands.
authors.forename: Maeike
authors.initials: M
authors.lastname: Zijlmans
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Jean
authors.initials: J
authors.lastname: Gotman
mesh_terms: D000200:Action Potentials; D000293:Adolescent; D000328:Adult; D000368:Aged; D004569:Electroencephalography; D004827:Epilepsy / Q000175:diagnosis / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012895:Sleep, REM
keywords: Electroencephalography; Epilepsy; High frequency oscillations; Non-invasive EEG; Ripples; Spikes