title: Temporal and spatial determination of EEG-seizure onset in the frequency domain.
abstract: OBJECTIVE
  A quantitative analysis of scalp electric fields in patients suffering from pharmacoresistant temporal lobe epilepsy was performed in order to study the development of rhythmic ictal activities over time.
  
  
  METHODS
  A method that calculates phase-corrected voltage maps in the frequency domain (FFT-approximation) was applied to ictal multichannel recordings in 10 epileptic patients. The onset of the ictally dominant frequency was determined and its temporal evolution over a time period of 46 s around the ictal EEG onset was studied. The analysis was completed by a linear inverse solution that estimated the sources of the dominant frequency.
  
  
  RESULTS
  This method permitted the identification of an ictally dominant frequency which started on the average prior to the onset of initial EEG signs as determined by visual inspection. The frequency incremented during the evolution of the seizure in all patients. The linear inverse solution algorithm localized the source of this frequency to the brain region which was clinically determined as the site of seizure onset and whose resection rendered all patients seizure-free.
  
  
  CONCLUSIONS
  Our data suggest that the constant increase of the ictally dominant frequency is related to the amount of temporal lobe tissue generating the ictal discharges. Frequential analysis of ictal electric fields can be reliably used to detect focal pathological activity early during seizure onset arising in deep structures such as the mesial temporal lobe.
authors.affiliation: Laboratory of Presurgical Epilepsy Evaluation, Department of Neurology, University Hospital, 24 rue Micheli-du-Crest, 1211, Geneva, Switzerland.
authors.forename: O
authors.initials: O
authors.lastname: Blanke
authors.forename: G
authors.initials: G
authors.lastname: Lantz
authors.forename: M
authors.initials: M
authors.lastname: Seeck
authors.forename: L
authors.initials: L
authors.lastname: Spinelli
authors.forename: R
authors.initials: R
authors.lastname: Grave de Peralta
authors.forename: G
authors.initials: G
authors.lastname: Thut
authors.forename: T
authors.initials: T
authors.lastname: Landis
authors.forename: C M
authors.initials: CM
authors.lastname: Michel
mesh_terms: D000328:Adult; D004569:Electroencephalography / Q000379:methods; D004833:Epilepsy, Temporal Lobe / Q000473:pathology / Q000503:physiopathology*; D005074:Evoked Potentials, Visual; D006624:Hippocampus / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D012640:Seizures / Q000503:physiopathology; D013997:Time Factors; D014055:Tomography, Emission-Computed; D015899:Tomography, Emission-Computed, Single-Photon