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Brain Advance Access published online on April 21, 2009
Brain, doi:10.1093/brain/awp083
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© The Author (2009). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Brain regions underlying word finding difficulties in temporal lobe epilepsy

Agnes Trebuchon-Da Fonseca1,2, Eric Guedj2,3, F-Xavier Alario2,4, Virginie Laguitton5, Olivier Mundler2,3, Patrick Chauvel1,2,6 and Catherine Liegeois-Chauvel1,2

1 INSERM, U751, Marseille, F-13000, France 2 Aix-Marseille Université, Marseille, F-13000, France 3 Assistance Publique – Hôpitaux de Marseille, Hôpital de la Timone, Pôle d’Imagerie Médicale, Marseille, F-13000, France 4 CNRS, Laboratoire de Psychologie Cognitive, Marseille, F-13000, France 5 Hôpital Henri Gastaut, Marseille, F-13000, France 6 Assistance Publique – Hôpitaux de Marseille, Hôpital de la Timone, Pôle de Neurosciences Cliniques, Marseille, F-13000, France

Correspondence to: Agnes Trebuchon-Da Fonseca, INSERM U751, laboratoire Epilepsie et Cognition, Université de la Méditerranée, faculté de médecine Timone, 27, Bd Jean-Moulin – 13385, Marseille cedex 05, France E-mail: agnes.trebuchon{at}univmed.fr

Word finding difficulties are often reported by epileptic patients with seizures originating from the language dominant cerebral hemisphere, for example, in temporal lobe epilepsy. Evidence regarding the brain regions underlying this deficit comes from studies of peri-operative electro-cortical stimulation, as well as post-surgical performance. This evidence has highlighted a role for the anterior part of the dominant temporal lobe in oral word production. These conclusions contrast with findings from activation studies involving healthy speakers or acute ischaemic stroke patients, where the region most directly related to word retrieval appears to be the posterior part of the left temporal lobe. To clarify the neural basis of word retrieval in temporal lobe epilepsy, we tested forty-three drug-resistant temporal lobe epilepsy patients (28 left, 15 right). Comprehensive neuropsychological and language assessments were performed. Single spoken word production was elicited with picture or definition stimuli. Detailed analysis allowed the distinction of impaired word retrieval from other possible causes of naming failure. Finally, the neural substrate of the deficit was assessed by correlating word retrieval performance and resting-state brain metabolism in 18 fluoro-2-deoxy-D-glucose-Positron Emission Tomography. Naming difficulties often resulted from genuine word retrieval failures (anomic states), both in picture and in definition tasks. Left temporal lobe epilepsy patients showed considerably worse performance than right temporal lobe epilepsy patients. Performance was poorer in the definition than in the picture task. Across patients and the left temporal lobe epilepsy subgroup, frequency of anomic state was negatively correlated with resting-state brain metabolism in left posterior and basal temporal regions (Brodmann's area 20-37-39). These results show the involvement of posterior temporal regions, within a larger antero-posterior-basal temporal network, in the specific process of word retrieval in temporal lobe epilepsy. A tentative explanation for these findings is that epilepsy induces functional deafferentation between anterior temporal structures devoted to semantic processing and neocortical posterior temporal structures devoted to lexical processing.

Key Words: temporal lobe epilepsy; naming; anomia; cerebral metabolism; language

Abbreviations: BA, Brodmann's area; FDG-PET, fluoro-2-deoxy-D-glucose-Positron Emission Tomography; HS, hippocampal sclerosis; LTLE, left temporal lobe epilepsy; RTLE, right temporal lobe epilepsy; SPM, statistical parametric mapping; TLE, temporal lobe epilepsy.

Received November 4, 2008. Revised February 21, 2009. Accepted February 23, 2009.


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