1932] Poliak: Afferent Fiber Systems, Primate Cerehral Cortex 27 



Chapter V 



ORIGIN, COURSE, AND TERMINATION OF SOMATO-SENSORY 

 THALAMO-CORTICAL AND THALAMO-STRIATE FIBERS 



In four of my experiments, as far as the somatic sensory system is 

 concerned, I attempted to interrupt the thalamo-cortical radiation by 

 injuring the thalamus or by cuttinor the radiation itself close to the 

 thalamus (for Visual and Auditory central paths investig:ated in the 

 same cases, see corresponding' chapters). This was achieved in 

 Experiment I almost entirely by an intrathalamic lesion (L in figs. 28- 

 31, 33-36) ; in Experiment II the thalamo-cortical radiation was inter- 

 rupted chiefly within the internal capsule in the immediate vicinity 

 of the thalamus (L in figs. 48-51), and partly by an intrathalamic 

 lesion (figs. 50, 51) ; while in Experiment III and V-a a portion of the 

 radiation was interrupted within the internal capsule exclusively 

 {L in figs. 5 and 66). In Experiment I a considerable part of the 

 radiation degenerated. In Experiment II probably a majority, if not 

 all of the fibers of the thalamic radiation degenerated ; while in Experi- 

 ment III only the posterior or caudal half of the radiation, and in 

 Experiment V-a only the intermediate segment of the radiation 

 degenerated. 



The primary object of these experiments was to produce as com- 

 plete as possible a degeneration of the entire central portion of the 

 somatic sensory path and, using Marchi's method, to determine the 

 "minimal" cortical region of the hemisphere supplied by fibers of 

 thalamic origin. Next it was intended to determine the origin, course, 

 and termination of parts of the thalamo-cortical radiation as well as 

 to delimit cortical areas where such individual bundles of the radia- 

 tion terminate. The third object of the investigation was to study 

 minute relations of the afferent somato-sensory fibers to cortical 

 structures. 



Experiment I 



In Experiment I a lesion was produced by plunging a small 

 Graefe's knife into the spot indicated in figure 1 as a small dotted 

 area in the lowermost part of the angular convolution, close to the 

 sulcus occipitalis inferior. The instrument was directed mesially and 



