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Somatosensory cortex; Shape perception; Positron emission tomography (PET); Curvature perception; Cytoarchitectural areas 3a, 3b, and 1; Human
Abstract:
Humans can easily by touch discriminate fine details of the
shapes of objects. The computation of representations and the
representations of objects differing in shape are, when the
differences are not founded in different sensory cues or the
objects belong to different categories, assumed to take place in
a series of cortical areas, which only show differences at the
single-neuron level. How the somatosensory cortex computes
shape is unknown, but theoretically it should depend heavily on
the curvatures of the object surfaces. We measured regional
cerebral blood flow (rCBF) of normal volunteers with positron
emission tomography (PET) as an index of neuronal activation.
One group discriminated a round set of ellipsoids having a
narrow spectrum of curvatures and an oblong set of ellipsoids
having a broad spectrum of curvatures. Another group discriminated
curvatures. When the rCBF from the conditions round
and oblong ellipsoid discrimination was contrasted, part of the
cortex lining the postcentral sulcus had significantly higher
rCBF when ellipsoids having a broader spectrum of curvatures
were discriminated. This cortex was also activated by curvature
discrimination. The activation is therefore regarded as crucial
for the computation of curvature and in accordance with curvature
being a major determinant of object form; this cortex is
also crucially active in somatosensory shape perception. A
comparison of the activation with cytoarchitectural maps, in the
anatomical format of the standard brain for both PET and
cytoarchitectural brain images, revealed that this part of the
cortex lining the postcentral sulcus is situated caudally from
cytoarchitectural area 1 and may involve presumptive area 2 on
the posterior bank of the sulcus.
