CYTOARCHITECTURE OF THE FERRET SUPRASYLVIAN GYRUS CORRELATED WITH AREAS CONTAINING MULTIUNIT RESPONSES ELICITED BY STIMULATION OF THE FACE

The cytoarchitecture was studied in a segment of the ferret suprasylvi an gyrus containing at least two and possibly four somesthetic represe ntations of the face that were observed in the primary somatosensory c ortex. These representations were restricted to the crown of the gyrus and were surrounded by somesthetically unresponsive cortex that exten ded down both sides to the base of adjacent sulci. Numerous cytoarchit ectonic subdivisions were found on a qualitative basis, and were confi rmed quantitatively by cluster analyses and relevant statistical tests of 10 prominent features from layers III, IV, and V. Four distinct cy toarchitectonic subdivisions, each with a well-developed and homogeneo us granular layer IV, were found distributed from anterior to posterio r along the crown of the gyrus at sites corresponding to the locations of the four facial representations. The surrounding unresponsive cort ex had a fragmented cytoarchitecture, especially along the medial bank and base of the coronal sulcus. This unresponsive cortex separated th e facial representations from the body representations, which were loc ated on the adjacent posterior cruciate gyrus. Most of the unresponsiv e subdivisions had a heterogeneous or agranular layer IV and fairly we ll-developed sublamination in layer III, which may be indicative of ex tensive corticocortical connections. One set of unresponsive subdivisi ons had comparable cytoarchitectures that directly bordered the facial representations. Another set of unresponsive subdivisions with compar able architectures occupied most of the lateral bank of the gyrus. The implications of multiple representations and cytoarchitectonic fragme ntation of the ferret primary somatosensory cortex are discussed in re lation to the organization of the primary somatosensory cortex in othe r species.