Brain Advance Access published online on December 5, 2008
Brain, doi:10.1093/brain/awn329
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Limitations to plasticity of language network reorganization in localization related epilepsy
1Department of Neurosciences, Children's National Medical Center, George Washington University School of Medicine, Washington, District of Columbia, 2Clinical Epilepsy Section NINDS, NIH, Bethesda, 3Department of Neurology, Johns Hopkins Hospital, Baltimore, Maryland, 4Department of Radiology, Children's National Medical Center, George Washington University School of Medicine, Washington, District of Columbia and 5Department of Neurology, Georgetown University School of Medicine, Baltimore, MA, USA
Correspondence to:
William Davis Gaillard, Department of Neuroscience, Children's National Medical Center, 111 Michigan Ave NW, Washington, District of Columbia 20010, USA E-mail: wgaillar{at}cnmc.org
Neural networks for processing language often are reorganized in patients with epilepsy. However, the extent and location of within and between hemisphere re-organization are not established. We studied 45 patients, all with a left hemisphere seizure focus (mean age 22.8, seizure onset 13.3), and 19 normal controls (mean age 24.8) with an fMRI word definition language paradigm to assess the location of language processing regions. Individual patient SPM maps were compared to the normal group in a voxel-wise comparison; a voxel was considered to be significant if its z-value exceeded |2|. Subsequently, we used principal component analysis with hierarchical clustering of variance patterns from individual difference maps to identify four patient sub-groups. One did not differ from normal controls; one had increased left temporal activation on the margin of regions activated in controls; two others had recruitment in right inferior frontal gyrus, middle frontal gyrus and temporal cortex. Right hemisphere activation in these two groups occurred in homologues of left hemisphere regions that sustained task activation. Our study used novel data driven methods to find evidence for constraints on inter-hemispheric reorganization of language in recruitment of right homologues, and, in a subpopulation of patients, evidence for intra-hemispheric reorganization of language limited to the margins of typical left temporal regional activation. These methods may be applied to investigate both normal and pathological variance in other developmental disorders and cognitive domains.
Key Words: fMRI; language; epilepsy
Abbreviations: ECS, Electro-cortical stimulation; MTG, mid temporal gyrus; MTS, mesial temporal sclerosis; PCA, principal components analysis
Received May 21, 2008. Revised October 31, 2008. Accepted November 9, 2008.