The somatotopy of speech: Phonation and articulation in the human motor cortex

Department of Psychology, Simon Fraser University, Burnaby, BC, Canada.
Brain and Cognition (Impact Factor: 2.48). 02/2009; 70(1):31-41. DOI: 10.1016/j.bandc.2008.12.006
Source: PubMed


A sizable literature on the neuroimaging of speech production has reliably shown activations in the orofacial region of the primary motor cortex. These activations have invariably been interpreted as reflecting "mouth" functioning and thus articulation. We used functional magnetic resonance imaging to compare an overt speech task with tongue movement, lip movement, and vowel phonation. The results showed that the strongest motor activation for speech was the somatotopic larynx area of the motor cortex, thus reflecting the significant contribution of phonation to speech production. In order to analyze further the phonatory component of speech, we performed a voxel-based meta-analysis of neuroimaging studies of syllable-singing (11 studies) and compared the results with a previously-published meta-analysis of oral reading (11 studies), showing again a strong overlap in the larynx motor area. Overall, these findings highlight the under-recognized presence of phonation in imaging studies of speech production, and support the role of the larynx motor cortex in mediating the "melodicity" of speech.

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    • "This represents a striking species difference in the cortical control of the larynx between monkeys and humans, one supported by neuroanatomy. In monkeys, the cortical larynx area is restricted to the premotor cortex (Hast et al., 1974), while in the human brain it extends into primary motor cortex as well (Loucks et al., 2007; Brown et al., 2008; Simonyan et al., 2009; Belyk and Brown, 2014b). The human larynx area is activated by volitional movement of the laryngeal muscles, phonation and forced expiration, leading us to refer to it as the 'larynx phonation area' (LPA; Brown et al., 2008). "
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    • "Weaker connectivity in patients between IFG and the right PT, and bilateral superior parietal regions supports this claim, suggesting suboptimal communication between frontal areas associated with overall language planning (IFG) and temporal and parietal sensory-motor integration (PT, superior parietal region). Furthermore, patients showed stronger connectivity between the right insula and regions in the left PG and posterior MFG, and bilateral parietal areas, suggesting alterations in neural activity patterns related to motor speech planning and/or sensory-motor integration (Brown et al., 2009; Cauda et al., 2011; Price, 2010, 2012; Sahin et al., 2006). The question is whether this insula network has evolved in patients over time to compensate for lack of connectivity between IFG and PT/parietal areas. "
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    • "The high degree of laterality seen in WGEN tasks has been thought to be related in language production. Since the pure motor functions related in overt speech i.e. articulation and phonation as well as orofacial movements have been shown to produce bilateral activation in the human motor cortex (Brown et al., 2009; Grabski et al., 2012). The advantage of fMRI is the ability to illustrate the activated areas of the whole network (Rutten and Ramsey, 2010), including activations in more deeply located cortical areas as well, while direct brain stimulation methods, DCS and TMS, provide very local and discrete functional location affecting only a specific part of a neuronal network involved in speech production. "
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