1912.] 



Instability of Cortical Points. 



277 



inhibition. In our records it appears more prominent than excitation 

 itself. Often it manifests itself along with excitation as a reciprocal effect, 

 also, however, it occurs without obvious concomitant excitation of the 

 antagonistic muscle, and, so far as our experience at present goes, more often 

 than does the contrary phenomenon — namely, excitatory contraction without 

 concomitant inhibitory relaxation of the opponent. This feature of the 

 records inclines us to suppose that the inhibitory and excitatory effects 

 respectively — although with great frequency reciprocally yoked together 

 under cortical stimulation — are, as cortical reactions, nevertheless, to a 

 considerable extent independently exhibitable. In regard to this, however, 

 it has, of course, to be remembered that our observations have of necessity 

 been confined to a particular muscle-pair as a sample of the whole limb 

 musculature. Were it possible to survey contemporaneously more of the 

 several muscles of the limb, the wider field of observations might possibly 

 reveal closer concomitance between the two effects. In some cases the 

 records exhibit concomitant increase of contraction in both of the component 

 muscles ; in such cases it may well be that double reciprocal innervation is 

 at work — as has been pointed out, that phenomenon may quite reasonably 

 be expected as a reaction from a cortical point. But it must be admitted 

 that as yet no experimental proof has been given that it actually is so. 



In directing attention to the frequency of temporary changes in the effect 

 exerted by a cortical point upon an antagonistic muscle-pair, and in shewing 

 that these changes not rarely reach actual reversal of the sense of the 

 movement, we would not be understood as impugning the general 

 regularity of the results which such cortical points yield when appropriately 

 examined. The same cortical point, returned to after a period of quiescence, 

 will usually, time after time, yield approximately the same result on the 

 muscle-pair with considerable consistency. What we desire to stress in 

 regard to the reaction of the cortical point on the antagonistic muscle-pair 

 is the influence of shortly pre-current excitations, both of itself and of other 

 points, and of afferent channels. And in this respect the functional 

 instability of some cortical points seems to be greater than that of others. 

 The instability is great enough to be easily demonstrable under narcosis as 

 in our experiments. It may well be even greater in normal conditions 

 without narcosis. Indeed, the frequence of reversal as a phenomenon 

 attaching to the reactions of points in the motor cortex suggests that one 

 of the functions of the cortex may be performance of reversals, and that the 

 greater predominance of reversal under cortical than in purely spinal or 

 decerebrate reflexes is because reversal is one of the specific offices of the 

 cortex cerebri. 



