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mapping of visual cortex
It is well established that a large fraction of the cerebral cortex is concerned with vision
(ref). The visual cortex is subdivided into multiple areas believed to play specialized roles
in the analysis of visual stimuli. Many of these areas are retinotopically organized, that is,
they have a direct correspondence to position on the retina. It as been shown that the
topology of the organization can be used to delimit the borders between the multiple visual
areas (ref). Localizing these borders may be critical to the proper interpretation of
functional imaging studies not only of vision per se, but of any task involving visual input.
The same applies as well to tasks which are not obviously visual but nevertheless produce
responses in visual cortex, e.g., tactile discrimination (Burton ref).
The basic method we use is relatively mature and was first described by Dale & Sereno (ref)
and independently by deYoe (ref). The method invloves expanding ring stimuli which produce
waves of activation moving parallel to the calcarine sulcus, and rotating sector stimuli which
produce activations perpendicular to the calcarine sulcus. Responses to eccentricity and
sector stimuli show an orthogonal pattern. The upper and lower hemifield responses appear on
opposite sides of the calcarine sulcus. These responses are those expected given the
well-known organization of the visual cortex.
The field sign method for retinotopic mapping requires having a representation of the cortical
surface. Cortical segmentation is a relatively new procedure with several groups actively
engaged in technical development. The laboratory of Dr. David Van Essen, with whom we are
collaborating, is one of the leaders in this field.
Efforts have been made to improve the quality of images sent through the segmentation process.
A summary of such work can be seen here.
RESULTS.
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