Page:Principles of Psychology (1890) v1.djvu/91

71 FUNCTIONS OF THE BRAIN 71 weeks into the same canine muscles into which it used to discharge before the operation. As far as the cortex itself goes, since one of the purposes for which it actually exists is the production of new paths,* the only question before us is : Is the formation of these particular ' vicarious ' paths too much to expect of its plastic powers ? It would cer- tainly be too much to expect that a hemisphere should receive currents from optic fibres whose arriving -place with- in it is destroyed, or that it should discharge into fibres of the pyramidal strand if their place of exit is broken down. Such lesions as these must be irreparable ivithin that hemisphere. Yet even then, through the other hemisphere, the corpus callosum, and the bilateral connections in the spinal cord, one can imagine some road by which the old muscles might eventually be innervated by the same in- coming currents which innervated them before the block. And for all minor interruptions, not involving the arriving- place of the 'cortico-petal' or the place of exit of the 'cortico- fugal' fibres, roundabout paths of some sort through the affected hemisphere itself must exist, for every point of it is, remotely at least, in potential communication with every other point. The normal paths are only paths of least resistance. If they get blocked or cut, paths formerly more resistant become the least resistant paths under the changed conditions. It must never be forgotten that a current that runs in has got to run out someivhere ; and if it only once succeeds by accident in striking into its old place of exit again, the thrill of satisfaction which the consciousness connected with the whole residual brain then receives will reinforce and fix the paths of that moment and make them more likely to be struck into again. The resultant feeling that the old habitual act is at last successfully back again, becomes itself a new stimulus which stamps all the exist- ing currents in. It is matter of experience that such feel- ings of successful achievement do tend to fix in our memory whatever processes have led to them ; and we shall have change our present preliminary conjecture that that is one of its essential uses, into an unshakable conviction.
 * The Chapters on Habit, Association, Memory, and Perception will