Lateralization of olfactory processing: Differential impact of right and left temporal lobe epilepsies Julie Hudry a , Philippe Ryvlin b,c,d , Anne-Lise Saive a , Nadine Ravel a , Jane Plailly a , Jean-Pierre Royet a, ⁎ a Olfaction: From Coding to Memory Team, Lyon Neuroscience Research Center, INSERM U1028, CNRS UMR 5292, University of Lyon, France b Department of Functional Neurology and Epileptology, Hospices Civils de Lyon, Lyon, France c TIGER, Neuroscience Research Center of Lyon, INSERM U1028, CNRS 5292, Lyon-1 University, Lyon, France d Department of Clinical Neurosciences, CHUV, Lausanne, Swizterland abstract article info Article history: Received 16 June 2014 Revised 26 June 2014 Accepted 29 June 2014 Available online xxxx Keywords: Olfaction Temporal lobe epilepsy Lateralization Olfactory processes were reported to be lateralized. The purpose of this study was to further explore this phe- nomenon and investigate the effect of the hemispheric localization of epileptogenic foci on olfactory deficits in patients with temporal lobe epilepsy (TLE). Olfactory functioning was assessed in 61 patients and 60 healthy con- trol (HC) subjects. The patients and HC subjects were asked to rate the intensity, pleasantness, familiarity, and edibility of 12 common odorants and then identify them. Stimulations were delivered monorhinally in the nostril ipsilateral to the epileptogenic focus in TLE and arbitrarily in either the left or the right nostril in the HC subjects. The results demonstrated that regardless of the side of stimulation, patients with TLE had reduced performance in all olfactory tasks compared with the HC subjects. With regard to the side of the epileptogenic focus, patients with left TLE judged odors as less pleasant and had more difficulty with identification than patients with right TLE, underlining a privileged role of the left hemisphere in the emotional and semantic processing of odors. Final- ly, irrespective of group, a tendency towards a right-nostril advantage for judging odor familiarity was found in agreement with a prominent role of the right hemisphere in odor memory processing. © 2014 Elsevier Inc. All rights reserved. 1. Introduction The importance of the temporal lobes in human olfaction was recog- nized as early as the 1890s with the observation that patients with tem- poral lobe epilepsy (TLE) were prone to olfactory auras and olfactory dysfunctions [1–4]. Patients with TLE typically have normal olfactory sensitivity but impaired complex olfactory function, as assessed by stan- dard tests of odor discrimination, recognition memory, identification, and naming [5–13]. These olfactory deficits are thought to reflect the presence of several abnormalities of temporal lobe structures and func- tions underlying seizure disorders [for review, see [14,15]]. However, the specific neural networks altered in patients with TLE with olfactory deficits are still unknown. Based on cognitive psychology concepts [16,17], we previously hy- pothesized that the ratings of intensity, pleasantness, familiarity, and edibility represent different olfactory judgments requiring activation from perceptual to semantic representation [18–20]. This assumption was supported by functional neuroimaging data showing the involvement of distinct neural networks – in terms of both structure and hemispheric specialization – in these olfactory judgment tasks [18,19,21]. For example, the left hemisphere is dominant in the judgment of odor pleasantness, and the right hemisphere is dominant during the fa- miliarity judgment, emphasizing the roles of these hemispheres in emo- tional and memory processing, respectively [22]. These olfactory tasks have also been used to detect impaired olfactory abilities in patients with Alzheimer's disease, those with schizophrenia, or those with Parkinson's disease and show patterns of disturbance specific to each pa- thology [23–25]. A unique feature of olfactory system anatomy is that the olfactory nerve is the only cranial nerve with primarily ipsilateral central projec- tions to the piriform cortex, amygdala, and entorhinal cortex, although a few contralateral projections have been noted via the lateral olfactory tract and the anterior commissure [26,27]. Secondary projections reach the hippocampus, ventral striatum, thalamus, and orbitofrontal and insular cortices. As several areas involved in olfactory processing are localized to the temporal lobes [for review, see [28–30]], it follows that unilateral TLE can offer new insights to better understand the differential temporal hemispheric contributions to the perceptual and semantic processing of odors. Using monorhinal stimulations and stan- dard olfactory tests, previous studies have shown that olfactory deficits are restricted to the nostril ipsilateral to the epileptogenic region [9,10] and indicated that in commissurotomized patients, each hemisphere is Epilepsy & Behavior 37 (2014) 184–190 ⁎ Corresponding author at: Olfaction: From Coding to Memory, Centre de Recherche en Neurosciences de Lyon (CRNL), CNRS UMR 5292, INSERM U1028, Université Lyon 1, 50 Avenue Tony Garnier, 69366 Lyon Cedex 07, France. Tel.: +33 4 37 28 74 95; fax: +33 4 37 28 76 01. E-mail address: royet@olfac.univ-lyon1.fr (J.-P. Royet). http://dx.doi.org/10.1016/j.yebeh.2014.06.034 1525-5050/© 2014 Elsevier Inc. 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