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Oscillatory dynamics of spoken language production
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Poster D11 in Poster Session D, Wednesday, October 25, 4:45 - 6:30 pm CEST, Espace Vieux-Port
Haya Akkad1, Daniel Bush4, Tae Twomey1,2, Robert Seymour2, Susanne Pelke1, Sasha Ondobaka1, Sven Bestmann2,3, Jenny Crinion1,2; 1Institute of Cognitive Neuroscience, University College London, 2Wellcome Centre for Human Neuroimaging, University College London, 3Institute of Neurology, University College London, 4Department of Neuroscience, Physiology and Pharmacology, University College London
Introduction: While the brain regions involved in word production have been identified, the neural mechanisms underlying conceptual and lexical retrieval remain unclear. Here, we used mangentoencephalography (MEG) during a picture naming task to examine the oscillatory dynamics of spoken word production. Picture naming is commonly used to test word production as it captures all levels of processing from semantics to lexical retrieval and articulation. Methods: 27 healthy older adults (age ≥50 years) completed an overt picture naming task during a MEG scan. Stimuli consisted of black and white line drawings of objects randomised to a clear (naming) or scrambled (control) condition. Stimuli were presented on the screen for 2s, preceded by a 2.5s fixation period. Participants were instructed to name the clear stimuli and respond ‘no’ when the scrambled stimuli appeared. The naming condition consisted of monosyllabic words with high naming agreement. The scrambled condition controlled for low-level visual input and motor output, but did not involve any object recognition and lexical retrieval processes. MEG analyses were conducted using SPM on response-locked epochs. Sources of the oscillatory activity were reconstructed using a beamformer. Neural oscillations within the spoken language network were identified by contrasting source reconstructed time-frequency data in the naming > control condition. We report results at a statistical threshold of FWE-corrected p < 0.05 at cluster and voxel level. Results: Sensor-level time-frequency results showed that picture naming, relative to control, induced delta/theta (2 – 6 hz) synchronisation 1.4s preceding response, followed by an alpha/beta (8 – 20 hz) desynchronization 0.6s preceding response. Source-level results showed delta/theta and alpha/beta activity were left hemisphere dominant. Delta activity localised to a fronto-temporo-parietal language network, including the left inferior frontal gyrus, supramarginal gyrus and superior temporal gyrus. Theta activity localised to regions of attention control in the medial-frontal gyrus and to areas of lexical retrieval in the superior/medial temporal gyrus and lingual gyrus. Beta desychronisation was widespread throughout the left hemisphere, involving both motor and language regions, while alpha appeared to desynchronise along the ventral ‘object recognition’ pathway in the visual cortex and inferior temporal gyrus. Significance: In this study, we identified the oscillatory signatures of conceptual and lexical retrieval during overt picture naming. Delta activity engaged a long-range fronto-temporo-parietal language network, while theta activity modulated attention and lexical processing mechanisms. We show that beta oscillations modulate memory, as well as motor, aspects of spoken word production. Finally, studies to date have been unclear on the differential role, if any, of alpha/beta activity in language production – our findings suggest that alpha activity may selectively engage the mapping of visual information to semantics in the left basal language areas. Future work will explore whether these oscillatory dynamics are altered in aphasic patients with anomia (picture naming difficulties) and if they can be modulated to improve speech abilities.
Topic Areas: Language Production,