Ventral primary motor cortex¶
This chapter covers the last step in the cortical hierarchy of speech production, the ventral aspect of primary motor cortex:
Ventral primary motor cortex¶
{Vigneau et al., 2006, #88117}
The cluster straddling the upper part of the RolS closely matches the mouth primary motor area, as identified by a previous meta-analysis (Fox et al., 2001). The contrasts that correspond to this cluster included covert and overt articulation of phonemes (Bookheimer et al., 2000), syllables (Wildgruber et al., 2001), letters (Jessen et al., 1999), and pseudo-words (Riecker et al., 2000), as well as word repetition (Price et al., 1996c), and silent rehearsal of letters during working-memory tasks (Cohen et al., 1997 and Rypma et al., 1999). This area shows an asymmetry favoring left hemisphere activity, attesting to its specialization for language, and is correlated with syllable rate production (Fox et al., 2000). The fact that the leftward asymmetry decreases as the frequency of syllable production increases (Wildgruber et al., 2001) indicates a contribution to low-level aspects of speech motor control. Not only the production but also auditory discrimination of syllables (Hickok and Poeppel, 2004) activates this motor area, showing that the perception of syllables is achieved through the simulation of the motor activity necessary to produce the corresponding syllable. This hypothesis is confirmed both by a recent report showing that listening to syllables activates motor areas at the same location as RolS, which was shown to be involved during speech production in the same subjects (Wilson et al., 2004). It is also strengthened by the evidence of activation of articulation muscles during speech listening (Fadiga et al., 2002), resulting from transcranial magnetic stimulation study.
The lower precentral cluster (Prec) gathers peaks that show greater activity during phonological than semantic tasks, such as reading pseudo-words versus reading words (Herbster et al., 1997), detecting pseudo-words versus detecting words (Kotz et al., 2002), detecting rhymes versus detecting synonyms (Roskies et al., 2001), phonetic monitoring versus word and pseudo-word listening (Zatorre et al., 1992), and syllable counting versus word categorization (Poldrack et al., 1999). Because tongue (Riecker et al., 2000) and complex oro-laryngeal movements (Braun et al., 1997) also recruit this area, its involvement in phonology probably reflects the silent rehearsal component that is common to all of these tasks, as well as working-memory tasks (Bunge et al., 2001, Cohen et al., 1997, Hautzel et al., 2002, Paulesu et al., 1993 and Rypma et al., 1999).
Summary¶
References¶
Vigneau, M., Beaucousin, V., Hervé, P. Y., Duffau, H., Crivello, F., Houdé, O. et al. (2006). Meta-analyzing left hemisphere language areas: Phonology, semantics, and sentence processing. NeuroImage, 30(4), 1414-1432.
Hickok, G. (2012). Computational neuroanatomy of speech production. Nature Reviews Neuroscience, 13(2), 135-145.