Converging evidences on language impairment in Landau–Kleffner Syndrome revealed by behavioral and brain activity measures: A case study Ferenc Honbolygo ´ a, * , Vale ´ria Cse ´pe a , Attila Feke ´sha ´zy b , Miklo ´s Emri b , Tere ´z Ma ´ria ´n b , Gergely Sa ´rko ¨zy c , Roza ´lia Ka ´lma ´nchey c a Research Institute for Psychology, Hungarian Academy of Sciences, Department of Psychophysiology, Research Group of Developmental Psychophysiology, H-1068, Szondi u. 83-85, Budapest, Hungary b PET Centre, University Debrecen, Debrecen, Hungary c Semmelweis University Budapest, 2nd Department of Pediatrics, Divison of Neurology, Budapest, Hungary Accepted 13 October 2005 Available online 4 January 2006 Abstract Objective: To assess the linguistic abilities of a boy having Landau–Kleffner Syndrome, and relate the focal disturbance of brain activity due to epilepsy to the cognitive and linguistic deficits. Methods: Several kinds of assessments were carried out, including epileptic source analysis using electronic source localization methods and PET, neuropsychological assessment of cognitive functions, and assessment of speech perception skills (discrimination of phonetic and stress cues) using ERPs. Results: The source of epileptic activity was localized in the left superior temporal lobe. The neuropsychological assessment showed dissociation between verbal and nonverbal functions, and the performance in former was bellow the normal range. ERPs obtained to the processing of phonetic and stress speech cues indicated that the two cues were processed asymmetrically: the mismatch negativity component (MMN) was obtained for the phoneme difference, but not for the stress pattern difference. Conclusions: Our data converged as it showed that the patient presented a selective impairment of the language system, and the verbal working memory system appeared to be especially defective. It is suggested that the language deficit is at least partly due to the focal disturbance of those neural networks that underlie the functioning of the working memory system. Significance: LKS is a childhood language disorder that might serve as a model in studying what happens to the language system if, in the course of development, the essential neural circuits are severely disturbed. q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Childhood epilepsy; Acquired aphasia; Spike-and-wave activity; Phoneme discrimination; Stress perception; MMN 1. Introduction 1.1. The Landau–Kleffner Syndrome Landau–Kleffner Syndrome (LKS) is a rare childhood epilepsy accompanied by acquired aphasia. The first LKS cases were described by Landau and Kleffner (1957). They reported five children with a gradual regression of language abilities showing paroxysmal unilateral or bilateral spike- and-wave discharges, which were characteristically loca- lized in the temporo-parietal brain regions. The syndrome is relatively uncommon: in a review Ansink et al. (1989) report about 170 known LKS cases, and since then, this number has not increased considerably. In a recent paper, Smith and Hoeppner (2003) mention 198 published cases. The question arises whether the low number of LKS patients is due to the lack of proper diagnosis. The diagnosis is rather problematic given that the epileptic activity does not always Clinical Neurophysiology 117 (2006) 295–305 www.elsevier.com/locate/clinph 1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2005.10.016 * Corresponding author. Tel.: C36 1 354 2290; fax: C36 1 354 2416. E-mail address: hf@cogpsyphy.hu (F. Honbolygo ´).