73° THE CEREBRAL CORTEX. 



there is more than one physico-anatoniical explanation possible of the 

 occurrence in some cases, especially where a lesion is large, of sensory 

 disturbances affecting the paralysed side. For, first, the occurrence of 

 a large lesion may undoubtedly, as suggested by Legroux and de Brim, 

 affect the vascular supply of portions of the brain even remote from the 

 part where the lesion itself occurs ; or, in the case of a tumour, the pres- 

 sure of the growth may make itself felt in remote parts. It is unquestion- 

 ably the case that in extensive removals of cerebral cortex the effect of 

 such removal may influence — temporarily if not permanently — even the 

 whole of the same side of the brain ; so that, for example, removal of the 

 frontal lobe in the monkey has been found to produce both general 

 hemianaesthesia and hemianopsia, 1 and removal of the whole motor 

 area at one operation the same combination of sensory disturbances. 2 

 Secondly, defects of sensibility in a paralysed limb may be pro- 

 duced by the local effects of lymph accumulation, due to the loss of 

 activity of the muscles of the part (see p. 727). And there is yet 

 another way in which sensory defects indirectly following lesions of the 

 motor region may be explained, — one which also offers an explanation 

 of the fact that excitation of the Eolandic region of the brain is some- 

 times found to produce slight sensory symptoms, 3 and also perhaps of 

 the sensory " signal " which in some cases heralds the approach of an 

 epileptiform fit originating in the same region. For since the volitional 

 movements are guided and governed by afferent impressions received 

 from all parts — from the skin, the muscles themselves and their tendons, 

 and the other structures in the limbs which are affected by their action, 

 the eye, the ear, and other special sense organs — it is certain that the 

 parts of the cortex from which the volitional impulses emanate must by 

 means of association fibres be in intimate connection with those parts of 

 the cortex — some of which are known and others still unknown — which 

 are involved in the perception of such sensory impressions. These 

 association fibres must be assumed to be derived from cells in the 

 sensory parts of the cortex, and since when a nerve fibre is stimulated 

 conduction is in either direction, stimulation of the endings of these 

 association fibres in the motor region may affect the sensory parts 

 of the cortex through them. Further, it is a well-established fact 

 that the severance of a nerve fibre, not only produces the Wallerian 

 degeneration in its peripheral part, but also causes degenerative 

 changes in the cell from which it takes origin ; and especially is this 

 the case with sensory cells, where these degenerative changes may 

 proceed to complete atrophy. 4 We should therefore expect that even 



1 Ferrier and Turner, Phil. Trans., London, 1898, vol. cxc. B, pp. 35, 36. 



2 Mott, Journ. Physiol., Cambridge and London, 1892, vol. xv. p. 483, Exp. v. 



3 W. B. Ransom (Brain, London, 1892, vol. xv. p. 440) produced with a slight strength 

 of current in a patient who had been trephined, and whose brain was stimulated by needle 

 electrodes passed through the skin, a tingling sensation, in the part, which would contract 

 when the strength of the current was increased. No effect was observed on tactile 

 sensation. The effect may have been a vasomotor one. Cf. also C. L. Dana, Med. Bee., 

 N. Y., 1893, p. 578, who in a similar experiment found that, simultaneously with the 

 movement, a sensation of numbness and heaviness was produced in the limb moved 

 (opposite arm), similar to the sensation experienced when a peripheral nerve is pressed. 

 It is noteworthy that in neither case was the "idea of movement" called up, nor even 

 such sensations as ordinarily accompany movement. The movements produced in Dana's 

 case were very extensive, and with stronger stimulation were followed by general epileptic 

 convulsions and loss of consciousness ; prior to this the same numbness was felt in the 

 opposite arm and shoulder, which were the parts first moved. 



4 Of. article " Nerve Cell," this volume, p. 601. 



