Monday, May 21, 2007

Where is area Spt?

We occasionally get questions regarding how to define area Spt -- the key dorsal-stream region we believe performs sensory-motor transformations for speech. The acronym stands for Sylvian parietal temporal to reflect the fact that it is located within the Sylvian fissure at the parietal-temporal boundary. The region involves a portion of the planum temporal/parietal operculum (very hard to distinguish the two), and is a subportion of area tpt. For those interested in more detail, below is a definition that we included in a recently submitted manuscript. My former student, Brad Buchsbaum can provide more details regarding typical locations in standardized space.

Spt is functionally defined within an anatomically constrained region of interest. It was initially identified in an anatomically unconstrained analysis that specified regions showing both auditory (speech responsive) and motor (responsive during covert speech production) response properties (Buchsbaum et al. (2001), Hickok et al. (2003)). A network of regions is identified in such an analysis including area 44 and a more dorsal pre-motor site in the frontal lobe, a region in the superior temporal sulcus, and a region in the posterior aspect of the planum temporale, sometimes extending up into the parietal operculum. Anatomically this latter area, Spt, appears to be a sub-portion of Galaburda and Sanides’ (1980) area Tpt. Although auditory-motor responses are identifiable within this region very consistently in individual subjects (using their own anatomy as a guide to localization), the activation location in standardized space can vary substantially, due the extensive anatomical variability of the posterior Sylvian region. Thus Spt is defined as a region with the posterior portion of the Sylvian fissure that exhibits both auditory and motor response properties.


Brad Buchsbaum said...

Spt happens to be located in a region that has considerable anatomical variability from subject to subject. In some people the Sylvian fissure slants sharply upwards, and in others it diverges into ascending and descending branches. Putting that complexity aside, when you warp enough brains to Talairach space, Spt (or its central tendency) emerges at the magical Talaraich coordinates: x=-50, y=38, z=20, plus or minus 3mm.

I might elaborate on the localization of Spt in a more extensive blog entry, moderators permitting.

Jerry said...

just want to correct the typo: the coordinates should be negative on the y-axis, so Spt is rather located around [-50 -38 +20]

Michel said...

Damn, I always called this area Temporo Parietal Junction (TPJ)... what a dumb I am !