title: Hemodynamic Response to Interictal Epileptiform Discharges Addressed by Personalized EEG-fNIRS Recordings.
abstract: OBJECTIVE
  We aimed at studying the hemodynamic response (HR) to Interictal Epileptic Discharges (IEDs) using patient-specific and prolonged simultaneous ElectroEncephaloGraphy (EEG) and functional Near InfraRed Spectroscopy (fNIRS) recordings.
  
  
  METHODS
  The epileptic generator was localized using Magnetoencephalography source imaging. fNIRS montage was tailored for each patient, using an algorithm to optimize the sensitivity to the epileptic generator. Optodes were glued using collodion to achieve prolonged acquisition with high quality signal. fNIRS data analysis was handled with no a priori constraint on HR time course, averaging fNIRS signals to similar IEDs. Cluster-permutation analysis was performed on 3D reconstructed fNIRS data to identify significant spatio-temporal HR clusters. Standard (GLM with fixed HRF) and cluster-permutation EEG-fMRI analyses were performed for comparison purposes.
  
  
  RESULTS
  fNIRS detected HR to IEDs for 8/9 patients. It mainly consisted oxy-hemoglobin increases (seven patients), followed by oxy-hemoglobin decreases (six patients). HR was lateralized in six patients and lasted from 8.5 to 30 s. Standard EEG-fMRI analysis detected an HR in 4/9 patients (4/9 without enough IEDs, 1/9 unreliable result). The cluster-permutation EEG-fMRI analysis restricted to the region investigated by fNIRS showed additional strong and non-canonical BOLD responses starting earlier than the IEDs and lasting up to 30 s.
  
  
  CONCLUSIONS
  (i) EEG-fNIRS is suitable to detect the HR to IEDs and can outperform EEG-fMRI because of prolonged recordings and greater chance to detect IEDs; (ii) cluster-permutation analysis unveils additional HR features underestimated when imposing a canonical HR function (iii) the HR is often bilateral and lasts up to 30 s.
authors.affiliation: Multimodal Functional Imaging Laboratory, Biomedical Engineering Department, Montreal Neurological Institute, McGill University Montreal, QC, Canada.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Pellegrino
authors.affiliation: Multimodal Functional Imaging Laboratory, Biomedical Engineering Department, Montreal Neurological Institute, McGill University Montreal, QC, Canada.
authors.forename: Alexis
authors.initials: A
authors.lastname: Machado
authors.affiliation: Multimodal Functional Imaging Laboratory, Biomedical Engineering Department, Montreal Neurological Institute, McGill University Montreal, QC, Canada.
authors.forename: Nicolas
authors.initials: N
authors.lastname: von Ellenrieder
authors.affiliation: Department of Neurology and Neurosurgery, Montreal Neurological Institute and Hospital Montreal, QC, Canada.
authors.forename: Satsuki
authors.initials: S
authors.lastname: Watanabe
authors.affiliation: Department of Neurology and Neurosurgery, Montreal Neurological Institute and Hospital Montreal, QC, Canada.
authors.forename: Jeffery A
authors.initials: JA
authors.lastname: Hall
authors.affiliation: Departement de Génie Electrique, Ecole de Technologie SupérieureMontreal, QC, Canada; Center of Advanced Research in Sleep Medicine, Hospital Du Sacre-CœurMontreal, QC, Canada; Centre de Recherches Mathematiques, University of MontréalMontreal, QC, Canada.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Lina
authors.affiliation: Department of Neurology and Neurosurgery, Montreal Neurological Institute and Hospital Montreal, QC, Canada.
authors.forename: Eliane
authors.initials: E
authors.lastname: Kobayashi
authors.affiliation: Multimodal Functional Imaging Laboratory, Biomedical Engineering Department, Montreal Neurological Institute, McGill UniversityMontreal, QC, Canada; Department of Neurology and Neurosurgery, Montreal Neurological Institute and HospitalMontreal, QC, Canada; Centre de Recherches Mathematiques, University of MontréalMontreal, QC, Canada; Physics Department and Perform Center, Concordia UniversityMontreal, QC, Canada.
authors.forename: Christophe
authors.initials: C
authors.lastname: Grova
keywords: EEG; MEG; epilepsy; fMRI; fNIRS; hemodynamic response; interictal epileptiform discharges