Brain Advance Access originally published online on June 23, 2005
Brain 2005 128(8):1811-1817; doi:10.1093/brain/awh533
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Functional MRI of the pre-ictal state
1 Brain Research Institute, Heidelberg West, Departments of 2 Medicine and 3 Radiology, The University of Melbourne and 4 Department of Neurology, Royal Children's Hospital, Parkville, Victoria, Australia and 5 Department of Clinical Neurosciences, University of Calgary, Alberta, Canada
Correspondence to: Professor Graeme Jackson, Brain Research Institute, Neurosciences Building, Austin Health, Banksia Street, West Heidelberg, Victoria, Australia 3081 E-mail: BRI{at}brain.org.au
The mechanisms underlying the transition from interictal to ictal states are poorly understood. Non-linear mathematical analysis of EEG frequency components has confirmed the presence of a pre-ictal state in focal epilepsy. We report on functional MRI (fMRI) analysis of the pre-ictal state in three patients with intractable focal epilepsy. Each subject had a typical partial seizure in the scanner while continuous blood oxygen level dependent (BOLD) fMRI images were acquired. The pre-ictal BOLD changes were first analysed by statistically comparing BOLD signals of two one-minute blocks. Further examination of the full time course was then performed. Each patient showed highly significant, focal BOLD signal changes. In Patient 1, a striking pre-ictal BOLD signal increase was seen over the region of the seizure focus identified on complementary epilepsy investigations. No significant BOLD signal decreases were observed. Patient 2 showed widespread pre-ictal BOLD increase contralateral to the presumed seizure focus, as well as a focal BOLD decrease near the presumed seizure focus. In Patient 3, pre-ictal BOLD increase was co-localized with the site of hyperperfusion seen on ictal single photon emission computed tomography (SPECT). However, this was contralateral to the seizure focus localization based on seizure symptomatology. No significant BOLD decreases were seen. The time course data in each patient studied showed change of the BOLD signal several minutes before the onset of the seizure. Highly significant BOLD fMRI signal changes occur before the onset of seizures, supporting the presence of a pre-ictal state. These changes can be localized to the site of the presumed seizure focus, as well as to other brain regions, suggesting that the pre-ictal BOLD signal changes and their underlying mechanisms are complex.
Key Words: pre-ictal; functional MRI; epilepsy; seizure; EEG; magnetic resonance
Abbreviations: BOLD = blood oxygen level dependent; ECD = [(99m)Tc]technetium-ethylene cysteine dimer; FDG = [2-18F]fluoro-2-deoxyglucose; FLAIR = fluid-attenuated inversion-recovery; fMRI = functional MRI; GRE-EPI = gradient-recalled echo planar imaging; SPECT = single photon emission computerized tomography; SSMA = supplementary sensorimotor area; VEM = video-electroencephalographic monitoring
Received October 5, 2004. Revised March 19, 2005. Accepted April 4, 2005.
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