Brain Advance Access originally published online on December 5, 2005
Brain 2006 129(2):346-351; doi:10.1093/brain/awh694
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Left hippocampal pathology is associated with atypical language lateralization in patients with focal epilepsy
Departments of 1 Epileptology and 2 Radiology, University of Bonn and 3 Department of Diagnostic and Therapeutic Neuroradiology, Medical Center Bonn, Bonn, Germany, 4 Academic Neurology Unit, Division of Genomic Medicine, University of Sheffield, Royal Hallamshire Hospital, Sheffield, UK and 5 F.C. Donders Center for Cognitive Neuroimaging and Department of Neurology, Radboud University Nijmegen, Nijmegen, The Netherlands
Correspondence to: Dr Bernd Weber, Department of Epileptology, Sigmund Freud Street 25, 53105 Bonn, Germany E-mail: Bernd.Weber{at}ukb.uni-bonn.de
It is well recognized that the incidence of atypical language lateralization is increased in patients with focal epilepsy. The hypothesis that shifts in language dominance are particularly likely when epileptic lesions are located in close vicinity to the so-called language-eloquent areas rather than in more remote brain regions such as the hippocampus has been challenged by recent studies. This study was undertaken to assess the effect of lesions in different parts of the left hemisphere, lesions present during language acquisition, on language lateralization. We investigated 84 adult patients with drug-resistant focal epilepsy with structural lesions and 45 healthy control subjects with an established functional MRI language paradigm. Out of the 84 patients 43 had left hippocampal sclerosis, 13 a left frontal lobe lesion and 28 a left temporal-lateral lesion. All these lesions were likely to have been present during the first years of life during language acquisition. To assess the lateralization of cerebral language representation globally as well as regionally, we calculated lateralization indices derived from activations in four regions of interest (i.e. global, inferior frontal, temporo-parietal and remaining prefrontal). Patients with left hippocampal sclerosis showed less left lateralized language representations than all other groups of subjects (P < 0.005). This effect was independent of the factor of region, indicating that language lateralization was generally affected by a left hippocampal sclerosis. Patients with left frontal lobe or temporal-lateral lesions displayed the same left lateralization of language-related activations as the control subjects. Thus, the hippocampus seems to play an important role in the establishment of language dominance. Possible underlying mechanisms are discussed.
Key Words: fMRI; language; epilepsy; hippocampus
Abbreviations: AVM = arteriovenous malformation; DNT = dysembryoblastic neuroepithelial tumour; FCD = focal cortical dysplasia; FFE = fast field echo; fMRI = functional MRI; ROIs = regions of interest; TSE = turbo spin echo; TSE sequence = sagittal T1-weighted 3D gradient echo sequence
Received September 1, 2005. Revised October 10, 2005. Accepted October 24, 2005.
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