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Aging Modulates the Hemispheric Specialization during Word Production

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Aging Modulates the Hemispheric
Specialization during Word

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