From Phonemes to Articulatory Codes: An fMRI Study of the Role of Broca's Area in Speech Production

Institute for Adaptive and Neural Computation, University of Edinburgh, UK.
Cerebral Cortex (Impact Factor: 8.67). 02/2009; 19(9):2156-65. DOI: 10.1093/cercor/bhn239
Source: PubMed


We used event-related functional magnetic resonance imaging to investigate the neuroanatomical substrates of phonetic encoding and the generation of articulatory codes from phonological representations. Our focus was on the role of the left inferior frontal gyrus (LIFG) and in particular whether the LIFG plays a role in sublexical phonological processing such as syllabification or whether it is directly involved in phonetic encoding and the generation of articulatory codes. To answer this question, we contrasted the brain activation patterns elicited by pseudowords with high- or low-sublexical frequency components, which we expected would reveal areas related to the generation of articulatory codes but not areas related to phonological encoding. We found significant activation of a premotor network consisting of the dorsal precentral gyrus, the inferior frontal gyrus bilaterally, and the supplementary motor area for low- versus high-sublexical frequency pseudowords. Based on our hypothesis, we concluded that these areas and in particular the LIFG are involved in phonetic and not phonological encoding. We further discuss our findings with respect to the mechanisms of phonetic encoding and provide evidence in support of a functional segregation of the posterior part of Broca's area, the pars opercularis.

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    • "Riecker et al. observed an effect of syllable structure in the left posterior IFG and anterior insula and in the cerebellum (bilaterally), but they did not find any difference in activation for high versus low frequency syllables. Papoutsi et al. (2009) asked participants to repeat (overtly and covertly) pseudowords varying in the frequency of their syllables after a six-second delay. They observed a better accuracy for pseudowords with high frequency syllables along with increased activation in premotor areas, including the dorsal PrCG and the IFG, bilaterally, for low-relative to high-frequency pseudowords. "
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    ABSTRACT: The transformation of an abstract phonological code into articulation has been hypothesized to involve the retrieval of stored syllable-sized motor plans. Accordingly, gestural scores for frequently used syllables are retrieved from memory whereas gestural scores for novel and possibly low frequency syllables are assembled on-line. The present study was designed to test this hypothesis. Participants produced disyllabic pseudowords with high frequency, low frequency and non-existent (novel) initial syllables. Behavioral results revealed slower production latencies for novel than for high frequency syllables. Event-related potentials diverged in waveform amplitudes and global topographic patterns between high frequency and low frequency/novel syllables around 170ms before the onset of articulation. These differences indicate the recruitment of different brain networks during the production of frequent and infrequent/novel syllables, in line with the hypothesis that speakers store syllabic-sized motor programs for frequent syllables and assemble these motor plans on-line for low frequency and novel syllables.
    No preview · Article · Sep 2015 · Brain and Language
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    • "The association of TPJ activation with subvocal articulation that occurs automatically during speech perception, particularly when speech perception is challenging (Buchsbaum and D’Esposito, 2009; Price, 2010), comes from observations that TPJ activation increased when subjects articulated four versus two syllables during a task that involved delayed repetition and subvocal rehearsal of pseudowords (Papoutsi et al., 2009). This subvocal articulation/articulatory rehearsal account can explain activation in TPJ during auditory working-memory tasks (Buchsbaum and D’Esposito, 2009; Koelsch et al., 2009) but does not explain why TPJ activation has been reported for auditory imagery of sounds that cannot be articulated (see above). "
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    ABSTRACT: The aim of this paper was to investigate the neurological underpinnings of auditory-to-motor translation during auditory repetition of unfamiliar pseudowords. We tested two different hypotheses. First we used functional magnetic resonance imaging in 25 healthy subjects to determine whether a functionally defined area in the left temporo-parietal junction (TPJ), referred to as Sylvian-parietal-temporal region (Spt), reflected the demands on auditory-to-motor integration during the repetition of pseudowords relative to a semantically mediated nonverbal sound-naming task. The experiment also allowed us to test alternative accounts of Spt function, namely that Spt is involved in subvocal articulation or auditory processing that can be driven either bottom-up or top-down. The results did not provide convincing evidence that activation increased in either Spt or any other cortical area when non-semantic auditory inputs were being translated into motor outputs. Instead, the results were most consistent with Spt responding to bottom up or top down auditory processing, independent of the demands on auditory-to-motor integration. Second, we investigated the lesion sites in eight patients who had selective difficulties repeating heard words but with preserved word comprehension, picture naming and verbal fluency (i.e., conduction aphasia). All eight patients had white-matter tract damage in the vicinity of the arcuate fasciculus and only one of the eight patients had additional damage to the Spt region, defined functionally in our fMRI data. Our results are therefore most consistent with the neurological tradition that emphasizes the importance of the arcuate fasciculus in the non-semantic integration of auditory and motor speech processing.
    Full-text · Article · Jan 2014 · Frontiers in Human Neuroscience
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    • "This aligns nicely with our model, which implies increased influence between these regions during error processing. Additionally, Papoutsi et al. (2009) supports the existence of a ''dorsal stream'' proposed by Hickok for speech processing, which suggests that inferior frontal gyrus, premotor area and sPT are a core network in speech production (Papoutsi et al., 2009). Given this, it is possible that the similarities between the shift and no shift condition are indicative of the necessity of coupling between left IFG and left premotor cortex in vocalization. "
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    ABSTRACT: Introduction: This study aims to model connectivity of neural regions involved in voice control. Here, we used structural equation modeling on a published dataset that employed the pitch shift paradigm. We hypothesized that our models would confirm differences in connectivity related to superior temporal gyrus during error processing of vocalization. Methods: We extracted time course data of eight regions included from 10 healthy subjects. A detailed description of subjects, MRI scanning procedures, imaging acquisition and data analysis can be found in Parkinson et al. 2012. Effective connectivity of regions activated during shift and no-shift paradigms was assessed using structural equation modeling techniques (AMOS version 19.0, SPSS, IBM). Results Consistent with our hypothesis, STG appears to play a crucial role in vocalization and error processing, showing increased participation of the right hemisphere during the shift condition than the no shift condition. Furthermore, left inferior frontal gyrus displays significant contribution to the modulation of vocal control through connections with PMC that change in response to the shift condition. Conclusions: Results indicated changes in connectivity of the voice network related to error detection and correction. Our models indicate hemispheric sensitivity to different elements of the auditory feedback and highlight the importance of examining network connectivity.
    Full-text · Article · Nov 2013 · The Journal of the Acoustical Society of America
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