712 



THE CEREBRAL CORTEX. 



hand, may be associated with a total temporary deprivation of volitional 

 power, such as occurs in the condition known as hypnosis. 1 That 

 inhibition is an active function of the cortex, was shown by Bubnoff and 

 Heidenhain, 2 who occasionally got arrest of action on weak excitation. 

 More recently it has been proved by Sherrington 3 that electrical 

 excitation of certain parts of the cortex may not only, as has long been 

 known, produce contraction of definite muscles, but that simultaneously 

 inhibition of tonically contracted antagonists may be also brought about. 

 Thus if, after section of the third and fourth nerves on one side, say the 

 left, so that only the external rectus is left in connection with the 

 nerve centres, any of the parts of the left hemisphere which produce 

 conjugate deviation of the eyes to the right be stimulated, not only 

 does the right eye move to the right, but the left eye accompanies 

 it, as far, at least, as the primary position ; and this can, under 

 the circumstances, only be effected by the inhibition of the left 

 external rectus. 4 The same will occur during voluntary movements, 

 if the animal be kept alive a few days after the section of the 

 nerves. Moreover, it is a familiar fact that we are constantly in 

 the habit of exercising voluntary control over, and arresting reflex 

 movements ; and that this function is exercised by the cortex is 

 shown by its absence when from any cause the cortex is in abeyance, 

 e.g. during sleep. 5 



As to the manner in which inhibition is brought about, nothing is 

 definitely known. It has been suggested by Lauder Brunton, that it 

 may be regarded as a phenomenon analogous with that of interference 

 in physics, in which case it would not be necessary to assume the 

 existence of paths separate from those which conduct excitatory 

 impulses. But it is well known that in the case of peripheral inhibition 

 (heart, blood vessels), the paths are altogether different. And it has 

 been shown by Sherrington, that inhibition of a muscle or group of 

 muscles is not obtained by excitation of the same point of the cortex as 

 provokes their contraction, but rather in connection with the point from 

 which the contraction of the antagonist muscles is obtained, 6 so that it 

 appears certain that for this form of inhibition also there are separate 

 nervous paths from those concerned in causing movement. It is 

 probable that the action, whatever it may be, is exerted upon the lower 

 nerve centres in the cord and bulb. Gad, 7 with Orchansky, found that 



1 Inhibition through the cerebrum is not, however, the cause of the so-called hypnotism 

 of animals, of which the well-known experimentum mirabile of Kirscher may be taken as a 

 type, for Yerworn has shown that these effects are obtained equally well after removal of 

 the cerebrum (" Die sogen. Hypnose der Thiere," Jena, 1898). 



- Arch. f. d. ges. Physiol., Bonn, 1881, Bd. xxvi. 



3 Proc. Roy. Soc. London, 1893, vol. liii. p. 407; Joum. Physiol., Cambridge and 

 London, 1894, vol. xvii. p. 27 ; H. E. Hering and Sherrington, Arch. f. d. ges. Physiol., 

 Bonn, Bd. lxviii. S. 222; "Proc. Internat. Congress of Physiologists," Joum. Physiol., 

 Cambridge and London, 1898, vol. xxiii. (Suppl.). 



4 This has been confirmed by aid of the graphic method by Topolanski, Arch. f. Ophth,, 

 Leipzig, 1898, Bd. xlvi. S. 452. It applies equally to the limb muscles. The fact that 

 when one set of muscles contract the antagonists relax was noted by Charles Bell. 



5 According to the experiments of Fano upon the dog (Ccntralbl. f. Physiol., Leipzig 

 u. Wien, 1895, Bd. ix. S. 466, and Arch, ital. de bid., Turin, 1895, tome xxiv. p. 438, 

 removal of the whole frontal lobe, including the sigmoid gyrus, shortens the reaction time 

 of reflexes, while stimulation of that lobe lengthens the time, i.e. tends to inhibit reflex 

 movements. But destruction of the sigmoid gyrus alone produces no such effect. 



G See also H. E. Hering and Sherrington, Arch. f. d. ges. Physiol., Bonn, Bd. lxviii. 

 S. 222. 



7 " Verhandl. d. physio]. Gesellsch.," in Arch./. Physiol., Leipzig, 1887, S. 363. 



