title: Noncanonical spike-related BOLD responses in focal epilepsy.
abstract: Till now, most studies of the Blood Oxygen Level-Dependent (BOLD) response to interictal epileptic discharges (IED) have assumed that its time course matches closely to that of brief physiological stimuli, commonly called the canonical event-related haemodynamic response function (canonical HRF). Analyses based on that assumption have produced significant response patterns that are generally concordant with prior electroclinical data. In this work, we used a more flexible model of the event-related response, a Fourier basis set, to investigate the presence of other responses in relation to individual IED in 30 experiments in patients with focal epilepsy. We found significant responses that had a noncanonical time course in 37% of cases, compared with 40% for the conventional, canonical HRF-based approach. In two cases, the Fourier analysis suggested activations where the conventional model did not. The noncanonical activations were almost always remote from the presumed generator of epileptiform activity. In the majority of cases with noncanonical responses, the noncanonical responses in single-voxel clusters were suggestive of artifacts. We did not find evidence for IED-related noncanonical HRFs arising from areas of pathology, suggesting that the BOLD response to IED is primarily canonical. Noncanonical responses may represent a number of phenomena, including artefacts and propagated epileptiform activity.
authors.affiliation: Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, Queen Square, London, UK. l.lemieux@ion.ucl.ac.uk
authors.forename: Louis
authors.initials: L
authors.lastname: Lemieux
authors.forename: Helmut
authors.initials: H
authors.lastname: Laufs
authors.forename: David
authors.initials: D
authors.lastname: Carmichael
authors.forename: Joseph Suresh
authors.initials: JS
authors.lastname: Paul
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Walker
authors.forename: John S
authors.initials: JS
authors.lastname: Duncan
mesh_terms: D001921:Brain / Q000098:blood supply* / Q000473:pathology / Q000503:physiopathology; D001931:Brain Mapping; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods; D004828:Epilepsies, Partial / Q000473:pathology / Q000503:physiopathology*; D005260:Female; D005583:Fourier Analysis; D007839:Functional Laterality; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging; D008297:Male; D010100:Oxygen / Q000097:blood; D013997:Time Factors
chemical_list: D010100:Oxygen