title: Dynamic directed interictal connectivity in left and right temporal lobe epilepsy.
abstract: OBJECTIVE
  There is increasing evidence that epileptic activity involves widespread brain networks rather than single sources and that these networks contribute to interictal brain dysfunction. We investigated the fast-varying behavior of epileptic networks during interictal spikes in right and left temporal lobe epilepsy (RTLE and LTLE) at a whole-brain scale using directed connectivity.
  
  
  METHODS
  In 16 patients, 8 with LTLE and 8 with RTLE, we estimated the electrical source activity in 82 cortical regions of interest (ROIs) using high-density electroencephalography (EEG), individual head models, and a distributed linear inverse solution. A multivariate, time-varying, and frequency-resolved Granger-causal modeling (weighted Partial Directed Coherence) was applied to the source signal of all ROIs. A nonparametric statistical test assessed differences between spike and baseline epochs. Connectivity results between RTLE and LTLE were compared between RTLE and LTLE and with neuropsychological impairments.
  
  
  RESULTS
  Ipsilateral anterior temporal structures were identified as key drivers for both groups, concordant with the epileptogenic zone estimated invasively. We observed an increase in outflow from the key driver already before the spike. There were also important temporal and extratemporal ipsilateral drivers in both conditions, and contralateral only in RTLE. A different network pattern between LTLE and RTLE was found: in RTLE there was a much more prominent ipsilateral to contralateral pattern than in LTLE. Half of the RTLE patients but none of the LTLE patients had neuropsychological deficits consistent with contralateral temporal lobe dysfunction, suggesting a relationship between connectivity changes and cognitive deficits.
  
  
  CONCLUSIONS
  The different patterns of time-varying connectivity in LTLE and RTLE suggest that they are not symmetrical entities, in line with our neuropsychological results. The highest outflow region was concordant with invasive validation of the epileptogenic zone. This enhanced characterization of dynamic connectivity patterns could better explain cognitive deficits and help the management of epilepsy surgery candidates.
authors.affiliation: Functional Brain Mapping Lab, Department of Fundamental Neurosciences, University of Geneva, Geneva, Switzerland.
authors.forename: Ana
authors.initials: A
authors.lastname: Coito
authors.forename: Gijs
authors.initials: G
authors.lastname: Plomp
authors.forename: Mélanie
authors.initials: M
authors.lastname: Genetti
authors.forename: Eugenio
authors.initials: E
authors.lastname: Abela
authors.forename: Roland
authors.initials: R
authors.lastname: Wiest
authors.forename: Margitta
authors.initials: M
authors.lastname: Seeck
authors.forename: Christoph M
authors.initials: CM
authors.lastname: Michel
authors.forename: Serge
authors.initials: S
authors.lastname: Vulliemoz
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000503:physiopathology; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000503:physiopathology; D055815:Young Adult
keywords: Directed connectivity; Electrical source imaging; High-density EEG; Temporal lobe epilepsy; Weighted Partial Directed Coherence