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Brain regions that support accurate speech production after damage to Broca’s area
Diego Lorca Puls1,2,3, Andrea Gajardo Vidal1,2,4, PLORAS Team1, Marion Oberhuber1, Susan Prejawa5, Thomas M. H. Hope1, Alexander P. Leff6,7, David W. Green8, Cathy J. Price1; 1Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, 2Memory and Aging Center, University of California San Francisco, 3Department of Speech, Language and Hearing Sciences, Faculty of Medicine, Universidad de Concepcion, Chile, 4Faculty of Health Sciences, Universidad del Desarrollo, Chile, 5Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, 6Institute of Cognitive Neuroscience, University College London, 7Department of Brain Repair and Rehabilitation, UCL Queen Square Institute of Neurology, 8Department of Experimental Psychology, University College London
Broca’s area in the posterior half of the left inferior frontal gyrus has traditionally been considered an important node in the speech production network. Nevertheless, recovery of speech production has been reported, to different degrees, within a few months of damage to Broca’s area. Here we investigated the brain activation patterns that underlie accurate speech production following stroke damage to Broca’s area. By combining functional MRI and 13 tasks that place varying demands on speech production, brain activation was compared in (i) seven patients of interest with damage to Broca’s area, (ii) 55 neurologically-intact controls and (iii) 28 patient controls with left-hemisphere damage that spared Broca’s area. When producing accurate overt speech responses, the patients with damage to Broca’s area activated a substantial portion of the normal bilaterally distributed system. Within this system, there was a lesion-site-dependent effect in a specific part of the right cerebellar Crus I where activation was significantly higher in the patients with damage to Broca’s area compared to both neurologically-intact and patient controls. In addition, activation in the right pars opercularis was significantly higher in the patients with damage to Broca’s area relative to neurologically-intact controls but not patient controls. By further examining how right Crus I and right pars opercularis responded across a range of conditions in the neurologically-intact controls, we suggest that these regions play distinct roles in domain-general cognitive control. Finally, we show that enhanced activation in the right pars opercularis cannot be explained by release from an inhibitory relationship with Broca’s area (i.e. dis-inhibition) because right pars opercularis activation was positively related to left pars opercularis activation in the neurologically-intact controls. Our findings motivate and guide future studies to investigate (a) how exactly right Crus I and right pars opercularis support accurate speech production after damage to Broca’s area and (b) whether non-invasive neurostimulation to one or both of these regions boosts speech production recovery after damage to Broca’s area.