We have argued previously that the posterior-medial planum temporale is not part of auditory cortex, but instead is multisensory and subserves sensory-motor integration, much like sensory-motor integration areas in the parietal lobe (Pa & Hickok, 2008). (See also a previous post on the topic.) A new paper by Novraj Dhanjal, Richard Wise, and colleagues in J. Neurosci. provides additional evidence for this view.
In an fMRI experiment, they had subjects produce speech (either count or produce propositional utterances) or, in other conditions, make silent repetitive jaw or tongue movements. One would expect a sensory-motor integration area to show somatosensory responses during articulation as this is useful information in movement control (it helps to know where your articulators are), and indeed, sensory-motor integration areas in the parietal lobe of human and non-human primates, areas such as saccade-related LIP and the parietal reach region (PRR), show somato responses.
So does area Spt show somatosensory responses? Yes, according to this new study. The medial planum temporale activated for both the speech articulation and mouth movement conditions, whereas other speech-related areas such as the lateral STG/STS only activated for the speech conditions.
So now we have direct evidence that this portion of the planum temporale is multisensory, as our hypothesis predicts. This is also consistent with evidence from animal studies which have found that the posterior supratemporal plane in monkeys shows multisensory properties (Hackett, et al., 2007).
N. S. Dhanjal, L. Handunnetthi, M. C. Patel, R. J. S. Wise (2008). Perceptual Systems Controlling Speech Production Journal of Neuroscience, 28 (40), 9969-9975 DOI: 10.1523/JNEUROSCI.2607-08.2008
Troy A. Hackett, Lisa A. De La Mothe, Istvan Ulbert, George Karmos, John Smiley, Charles E. Schroeder (2007). Multisensory convergence in auditory cortex, II. Thalamocortical connections of the caudal superior temporal plane The Journal of Comparative Neurology, 502 (6), 924-952 DOI: 10.1002/cne.21326
J PA, G HICKOK (2008). A parietal–temporal sensory–motor integration area for the human vocal tract: Evidence from an fMRI study of skilled musicians Neuropsychologia, 46 (1), 362-368 DOI: 10.1016/j.neuropsychologia.2007.06.024