1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 227 



Chapter XX 



REMARKS ON FUTURE INVESTIGATION OF THE 

 CEREBRAL CORTEX 



One of the objects of the present work was to facilitate further 

 investig^ation. A few points in this connection may be mentioned. 



Some modem experimental psychological investigations have 

 apparently yielded results not easy to reconcile with the conception of 

 the striate area as the sole "gateway" of the cerebral cortex for all 

 afferent visual impulses. For practical reasons, in experiments on 

 brightness discrimination, for example, lower mammals have been 

 used almost exclusively. Yet it is well known that the visual system 

 in the higher mammals and in man, though essentially the same, differs 

 considerably from that in lower mammals where the mesencephalic 

 visual mechanisms are better developed (see for example Ramon y 

 Cajal, 1909-11, vol. II, p. 386 ; Monakow, 1914, p. 127 ; Ariens Kappers, 

 1920-21, vol. II, and Herrick, 1926 ; consider also the well developed 

 mesencephalic visual centers in the rabbit, organized according to the 

 strict localistic principle as found by Overbosch). It appears, there- 

 fore, probable that the retention of ability to form the habit of bright- 

 ness discrimination observed in some of the above mentioned experi- 

 ments where the striate area was destroyed on both sides, was due 

 rather to the activity of the lower, subcortical visual mechanisms, than 

 to the remainder of the cerebral cortex. Be this as it may, before they 

 are applied to higher mammals and to man, the results derived from 

 the study of the visual function in lower mammals might well be con- 

 firmed by experiments upon primates (complete ablation of the striate 

 area on both sides ! ) , and controlled by further experiments on rats, 

 comprising removal of the entire cerebral cortex of both hemispheres 

 with the preservation of the subcortical visual centers. 



Furthermore, the contradictory results of various physiological and 

 psycho-physiological experiments involving the removal of certain 

 cortical regions supposedly visual, auditory, or sensory in function 

 are easily explained in view of the present experiments. Only rarely 

 were the corresponding cortical centers actually completely removed 

 or destroyed. Usually a considerable portion of these remained intact 

 and this has lead, of course, to erroneous conclusions. (See for 



