1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 69 



factory explanation of the cortical somatic sensory function. As has 

 been shown, the * ' nuclear or focal zone ' ' of the somatic sensory cortex 

 in the monkey's brain, and possibly in man's as well (areas PA and 

 PB of Economo-Koskinas), does not correspond with the convexities 

 of either the posteentral or the precentral convolutions, but is entirely 

 sunk in the sulcus centralis. By reason of the close proximity of the 

 * ' focal zone ' ' and the posteentral cortex in general, which seems to be 

 essentially a conscious exteroceptive and probably conscious proprio- 

 ceptive mechanism, in the experiments where an attempt was made to 

 remove the precentral cortex separately, and in similar pathological 

 cases, occasionally some impairment of exteroceptive sensibility was 

 registered, suggesting a localization of that form of sensibility in the 

 precentral ''motor" cortex. In other experiments and analogous 

 pathological cases where the injury of the precentral cortex was suffi- 

 ciently far away from the "focal zone," symptoms not bearing the 

 conscious exteroceptive character and due to the peculiar character 

 of the "unconscious reflex sensibility" localized here, were not 

 properly recognized and the role of the precentral cortex in any form 

 of sensation was altogether denied. This problem appears to be well 

 within the sphere of the technical possibility of attack in an experi- 

 mental way, by injuries strictly limited to one or to a few adjoining 

 cytoarchitectural areas without injurj^ to the subcortical substance, as 

 it will be shown in one of further reports. (Compare fig. 77.) 



Taken all together, the present investigations clearly demonstrate 

 that some form or other of the receptive, somato-sensory function has 

 to be attributed also to the precentral agranular cortex. It is, how- 

 ever, a task for further physiological and clinical investigation to 

 disclose the true nature of the sensibility which must be localized in 

 this cortex. In carefully conducted experiments, when removing the 

 precentral cortex, special attention must be })aid to the "focal zone" 

 and its portion of the thalamo-cortical radiation. Further, if the 

 present anatomical experiments are repeated, the transverse segmenta- 

 tion of the thalamo-cortical radiation must be considered ; otherwise, 

 if either the posterior or the anterior fiber "fan" of the radiation 

 alone were interrupted and if the conclusion were drawn that the 

 entire thalamo-cortical radiation terminates in the postcentral region 

 only, or in the precentral region only, one would commit the same 

 error as some previous investigators. To obtain reliable and satisfac- 

 tory results it wdll be indispensable to produce as complete degenera- 

 tion as possible of the entire radiation. 



