66 University of California Piihlications in Anatomy ["^^oi- 



Chapter VIII 



FUNCTION AND DISTURBANCES OF THE SOMATO-SENSORY 



RADIATION AND OF THE SOMATO-SENSORY 



PROJECTION CORTEX 



From the above findings there can be no doubt that the somato- 

 sensory cortex, or properly, the cortical representation of the thalamus 

 occupies a considerably larger region than a narrow strip immediately 

 behind the sulcus centralis. The present experiments show that the 

 agranular precentral cortex (areas 4 and 6 of Brodmann) as well as 

 the postcentral and parietal granular cortex (areas 1, 2, 3, 5, 43 and a 

 part of area 7 of Brodmann) receive direct impulses from the thal- 

 amus, each region by way of its own portion of the thalamo-cortical 

 radiation (besides those impulses which reach the precentral cortex 

 from the postcentral by way of strong, short U-shaped association 

 fibers, and vice versa, and other impulses from the opposite hemi- 

 sphere by way of the callosal fibers, as other of my experiments show). 

 For that reason the precentral cortex, that is, both areas 4 and 6 of 

 Brodmann, cannot be regarded as a mere executor for the influences 

 arriving here from the surrounding areas, notably from the postcentral 

 cortex ; for, as the disclosed connections of the precentral cortex indi- 

 cate, that cortex, besides receiving impulses from the postcentral and 

 other regions and besides the motor performances, has an afferent or 

 receptor function of its own. In that sense the precentral region must 

 certainly be regarded as a true sensory-motor cortex. The present 

 view of a complete or, at any rate, an almost complete separation of the 

 cortical "sensorium" from the "motorium" (except certain "pos- 

 tural" movements found by Graham Brown, Vogt, and Foerster when 

 the postcentral cortex was stimulated) must, therefore, be replaced by 

 another and a more appropriate conception. It would, however, be an 

 error to return to the former viewpoint of the integral unitarians by 

 declaring the entire extensive precentral-postcentral region as a 

 sensory-motor mechanism, the * ' sensomotorium ' ' of Exner, Munk, and 

 others, everywhere uniformly organized and functionally equivalent. 

 Certainly the findings of the students of cortical cytoarchitecture and 

 myeloarchitecture, whose division of the Rolandic region into several 

 areas cannot reasonably be disputed, are opposed to such a view. Also 

 the present finding of differences in the number and course of the 



