1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 47 



Chapter VI 



EXTENT AND BOUNDARIES OF THE SOMATO-SENSORY 

 CORTEX 



It should be remarked at the outset that my investigations decidedly 

 plead for the acceptance of a far more extensive portion of the hemi- 

 sphere as a somatic sensory region (fig. 6) than that accepted by most 

 contemporary neurologists. It is secondary to the question as to what 

 special sensory function should be attributed to each of the particular 

 cytoarchitectural areas of this extensive region (see Chapters VIII, 

 IX). A wide extent of the somato-sensory region on both sides of the 

 sulcus centralis C is evident from Experiment I (fig. 1), from Experi- 

 menti II (fig. 2) and from Experiment V-a (fig. 4), and its extent 

 behind the central sulcus from Experiment III (fig. 3) ; (variously 

 shaded areas in the accompanying figures are those receiving various 

 numbers of thalamic fibers). 



Over the external face of the hemisphere, Experiment I (fig. 1) 

 shows a somewhat smaller extent of the somato-sensory cortex in front 

 of the central sulcus, that cortex reaching more oralward in Experi- 

 ment II (fig. 2). This is due to the fact that in Experiment II the 

 lesion is much larger, separating a greater portion of the thalamus 

 from the rest of the hemisphere (figs. 48-51), its oral end being also 

 more anterior than the lesion in Experiment I (the plane of fig. 48 

 corresponds to that of fig. 28). This resulted in a larger portion of 

 the anterior half of the thalamus being left normal in Experiment I 

 than in Experiment II. Consequently a smaller part of the thalamo- 

 cortical radiation, that is, of its rostral ''fans," degenerated in the 

 first experiment. In both Experiments I and II, the somatic sensory 

 region determined in this way comprises on the convex face of the 

 hemisphere the following cytoarchitectural areas of Brodmann : 1, 2, 

 and 3, or the entire postcentral region of Brodmann, then area 5, and 

 the oral portion of area 7 of the parietal region proper (compare also 

 Experiment III, fig. 3, where the most dorsal portion of area 7 also 

 belongs to the somato-sensory region). In front of the central sulcus 

 it is area 4 of Brodmann or the area gigantopyramidalis which in both 

 Experiments I and II, receives thalamo-cortical fibers (compare figs. 1, 

 2, and 3 with fig. 7). 



