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Aging Modulates the Hemispheric Specialization during Word Production

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Aging Modulates the Hemispheric Specialization during Word Production

Elena Hoyau1, Naila Boudiaf1, Emilie Cousin1,2, Cedric Pichat1, Nathalie Fournet3, Alexandre Krainik2,4, Assia Jaillard 2 and Monica Baciu1*

1CNRS LPNC UMR 5105, Laboratoire de Psychologie et Neurocognition, Université Grenoble Alpes, Grenoble, France, 2UMS IRMaGe CHU, Université Grenoble Alpes, Grenoble, France, 3LPNC UMR 5105, Université Savoie Mont Blanc, Chambéry, France, 4Grenoble Institute of Neuroscience, Université Grenoble Alpes, Grenoble, France

Although older adults exhibit normal accuracy in performing word retrieval and generation (lexical production; e.g., object naming), they are generally slower in responding than younger adults. To maintain accuracy, older adults recruit compensatory mechanisms and strategies. We focused on two such possible compensatory mechanisms, one semantic and one executive. These mechanisms are reflected at inter- and intra-hemispheric levels by various patterns of reorganization of lexical production cerebral networks. Hemispheric reorganization (HR) changes were also evaluated in relation to increase naming latencies. Using functional magnetic resonance imaging (fMRI), we examined 27 healthy participants (from 30 years to 85 years) during an object naming task, exploring and identifying task-related patterns of cerebral reorganization. We report two main results. First, we observed a left intrahemispheric pattern of reorganization, the left anterior-posterior aging (LAPA) effect, consisting of supplementary activation of left posterior (temporo-parietal) regions in older adults and asymmetric activation along the left fronto-temporal axis. This pattern suggests that older adults recruit posterior semantic regions to perform object naming. The second finding consisted of bilateral recruitment of frontal regions to maintain appropriate response times, especially in older adults who were faster performers. This pattern is discussed in terms of compensatory mechanism. We suggest that aging is associated with multiple, co-existing compensation and reorganization mechanisms and patterns associated with lexical production. Keywords: object naming, aging, fMRI, hemispheric specialization, LAPA, HAROLD