[688 



HANDBOOK OF PH1M. i[ i n A 



Ml ROl'HYSIOLOGY III 



PIG "i Electrophysiological investigation of the corticospinal connections in the monkey. Left: 

 Superimposed action potentials of the radial nerve following each stimulus in a train of shocks 

 'stimulation frequency, 20 per sec.) delivered to the forelimb subdivision of the right precentral 

 area. The records are obtained at different time intervals after the beginning of the stimulation. 

 I \ response of 5.5 msec, latency appears at the beginning of the stimulation period. 11: After 2 

 sec. stimulation, a response with a shorter latency (j.j msec.) is to be noted. D: This shortest re- 

 sponse becomes maxima] after .( sec stimulation. E: It then disappears progressively alter 8 sec. 

 continuous -.11111111.111111] from Brinhaid \ rtohm ii.M. Rivht: Map of the precentral area of t li<- 

 monkey with the position of the 25 different points which wen successively stimulated. The responses 

 were recorded in .1 from the contralateral thenar nerve; in /(, from the contralateral hypothenar 

 ner\e. i. in If drawn in continuous linn and in dashed Una circumscribe the points which when stimu- 

 lated give responses of 3 msec, latency and of 5 msec , respectively; dolled line indicates t In- lower 

 border of the H msec, 'latency field.' Note that the shorter latency field (direct corticomotoneur.il 



ci ections) for the thenar nerve (in A) dots not overlap with that for the hypothenar nerve (inB). 



[From Bernhard & Bolun 



direct monosynaptic corticomotoneuronal path. This 

 is in agreemenl with the histological data of Hon" & 

 I lull (")")>. This path uses .1 selected group of fibers 

 with vn\ rapid conduction rates coming from the 

 cortical keyboard. On the other hand, the cortical 



region from which the localized responses of short 

 latency can be obtained shows remarkably well- 

 localized muscular sectors (see fig. 5). Particularly 

 significant is the facl thai the action of this mono- 

 synaptic connection i-. effective only in the presence 



