1932] Poliak: Afferent Fiher Systems, Primate Cerebral Cortex 103 



in the brain of the monkey an elevation of the cortex comparable with 

 the transverse temporal convolution of Heschl of human anatomy can 

 also usually be seen. This most richly supplied zone represents the 

 "nuclear or focal zone" of the entire auditory projection cortex. 

 According to this finding:, the entire area 22 of Brodmami in the brain 

 of the monkey (compare with fig. 7) does not belong to the auditory 

 projection cortex but, at most, to only a portion of it. The remaining 

 and larger portion of area 22, as well as the entire areas 20 and 21 of 

 Brodmann, do not receive direct auditory or any other afferent fibers 

 from subcortical regions and must be regarded as cortical centers of a 

 higher order. However, all evidence speaks in favor of a more exten- 

 sive cortical projection area of the cochlea than a narrow strip cover- 

 ing the transverse convolution of Heschl or even a part of it. 



Besides the cortical area in the Sylvian fossa which undoubtedly 

 belongs to the auditory sphere (area a in fig. 10), it was foimd in one 

 of the experiments with an exceptionally lai^e subcortical injury-, that 

 the cortex along the posterior extremity of the Sylvian fissure as far 

 back as the vicinity of the simian fissure also receives afferent fibers 

 from the between-brain (area x in fig. 10) . However, it was not possible 

 to determine whether that posterior Sylvian receptive area also belongs 

 to the auditory projection cortex and is, perhaps, its caudal contin- 

 uation ; or whether it represents a special projection area of an 

 unknown significance. (In Minkowski's [1923] Experiment 4 the 

 antero-dorso-median portion of the internal geniculate bod.y, besides 

 the puhdnar and the dorso-lateral thalamic nucleus, degenerated after 

 the ablation of Brodmann 's areas 5, 7, and the neighboring portion of 

 area 22; see also his Experiment 5.) That latter receptive area is 

 also for the greater part hidden in the Sylvian fissure and receives 

 abundant afferent fibers of large caliber. 



Since there exists a single auditory radiation terminating in a 

 single cortical projection area of fairly small siz^, it is permissible 

 to conclude that all auditory impulses, in so far as they reach the cere- 

 bral cortex, must first pass that afferent path and its terminal cortex, 

 which is the auditory "gateway" of the entire hemisphere, no matter 

 what the special nature or quality of the auditory impulses may be. 

 Only from that region are the auditory impulses further distributed 

 to the surrounding cortex of the temporal, insular, and parieto- 

 occipital lobes, the latter regions being the seat of "higher" auditory 

 and associated processes. The question of what fiber systems mediate 

 this further process of distribution and diffusion of incoming auditory 



