204 Functional Interrelations o£ the Brain Stem 



direct projections from the cerebral cortex; indeed, they have become so 

 intimately linked with the motor functions of the higher cortical level that 

 in man and higher apes it is probably impossible for them to function in the 

 organization of motor acts without the cerebral cortex itself. The interrelation 

 between basal ganglia and the cortex has indeed become so close that they 

 appear to function as a homogeneous unit. The basis for these generalizations 

 comes from three lines of evidence: anatomical, electrical, and from studies 

 involving seriatim ablations of the cerebral cortex and the striatal nuclei. 



Anatomical Studies.— The anatomical evidence of interconnections between 

 cortex and basal ganglia is less impressive than the physiological. Nearly all 

 observers working with the Marchi technique, after ablation of areas 4 and 6 

 of the cerebral cortex, have found degenerating fibers passing into the caudate 

 and putamen, and some also into the globus pallidus. But with Marchi sec- 

 tions there is no absolute proof that the fibers actually end in the area in 

 which they are seen to disappear (Levin,^ Mettler^. A carefully controlled 

 study by Verhaart and Kennard,* in which individual areas were destroyed by 

 the thermocoagulation technique of Dusser de Barenne, indicated that fibers 

 from areas 4 and 6, and especially from the intermediate-strip area 4-s of 

 Marion Hines, passed into the striatum; but as with the earlier studies, there 

 was no certain proof that they terminated there. Ramon y Cajal* had described 

 corticostriatal fibers with silver preparation and he has also observed dichoto- 

 mizing fibers from corticospinal projections passing into the putamen at the 

 level of the internal capsule. These, however, were fine fibers which one could 

 not expect to follow by Marchi degeneration. 



Electrical Evidence.— T>usser de Barenne and McCulloch^ found that strych- 

 ninization of certain areas in the macaque's precentral cortex evoked con- 

 spicuous electrical activity in the striate nuclei. The observation was one of 

 challenging interest because of associated effects elsewhere in the cerebral 

 cortex, and because of the sharply circumscribed character of the response 

 in the striatum itself. The precentral convolution is divided into three pri- 

 mary areas: area 4, area 6, and an intermediate-strip region, first defined by 

 Marion Hines"' which has been designated "area 4-s."* When A4-S is strych- 

 ninized, spontaneous electrical activity in A4 disappears (see fig. 1) and its 

 threshold for stimulation rises. Dusser de Barenne and McCulloch pointed 

 out that this suppression of electrical activity by local strychninization is not 

 mediated transcortically, but by a complex circuit from A4-S to the caudate 

 nucleus, thence to the thalamus and from there back to area 4. The caudate 

 nucleus thus becomes specifically activated by stimulation of area 4-s; they 

 found furthermore that strychninization of areas 4 or 6 had no such effect 

 on the caudate. Isolated destruction of the caudate, and of no other part of 

 the basal ganglia, caused disappearance of the strychnine suppression from 

 area 4-s. 



* To distinguish arm, leg, and face, it has become customary to refer to the major sub- 

 divisions as L4, A4, F4, L4-S, etc., designating the leg, arm, and face regions respectively. 



