CEREBRAL FUNCTION IN LEARNING 115 



VI. THE STIMULABLE CORTEX AND THE CORPUS STRIATUM IN 

 RELATION TO DISTURBANCES OF MOTOR COORDINATION 



The investigations of the functional anatomy of the rat's brain 

 thus far reported have all pointed to an almost complete inter- 

 changeability of function among the different parts of the cortex, 

 and a complete and rapid recovery from the effects of cerebral 

 operation. But among the 60 odd rats which have been subjected 

 to operation and subsequent tests by Dr. Franz and the writer, 

 there have appeared 9 with a persistent hemiparesis. Ordi- 

 narily, paralytic symptoms clear up very quickly, if they appear 

 at all, in lower animals after cerebral destruction. In these ani- 

 mals, however, the paretic condition, affecting the fore and hind 

 limbs of one side with sometimes the face, seemed to be almost 

 permanent. Some of the paretic animals were kept under ob- 

 servation for four months and during this time made no percepti- 

 ble spontaneous improvement in motor coordination. This 

 persistent paresis is so strongly in contrast with the evanescent 

 loss of other functions after cerebral injury as to arouse a special 

 interest in its cause. Franz and the writer suggested a possible 

 relation of the paresis to lesions of the corpus striatum but the 

 material then available was not varied enough to settle the point. 

 The present experiments have produced six additional cases and 

 these give fairly conclusive evidence on the cause of the paresis. 



The hemiparesis is easily recognizable by inspection as a stiff- 

 ness, clumsiness, or weakness of the legs of one side. It usually 

 leads to marked disturbance of gait, such as rotation to the right 

 or left, but the direction of rotation has no constant relation to 

 the position of the paralysis. A somewhat more certain analysis 

 of the character of the motor disturbance was obtained by forcing 

 the animals to climb down a vertical stretch of wire netting. 

 Normal animals support their weight equally well with the feet 

 of either side. Paretic animals can grasp firmly only with the 

 feet of the sound side and fall if forced to turn so that the weight 

 must be supported by the paretic legs. This test was applied 

 only to animals in the later experiments and the data in these 

 are therefore the more reliable. 



