THE FUNCTIONS OF THE CEREBRAL CORTEX 293 



The correlations involved in the motor functions of speech appear to be 

 represented typically in only one hemisphere, though this is by no means 

 rigidly true. The corresponding structures in the other hemisphere may 

 cooperate in these functions normally, and after loss of speech from a uni- 

 lateral lesion speech may be reacquired by further education of the unin- 

 jured centers of the same or the opposite side. It has recently been shown 

 that Broca's convolution is often larger on the left side of the brain than on 

 the right side and that the average thickness of the cortex in this region is 

 greater on the left side. 



Various attempts have been made to localize each of the various types of 

 aphasia mentioned above in a specific part of the cortex, but with no con- 

 cordant results. Each of these functions is, of course, very complex, and a 

 small circumscribed cortical injury may disturb or temporarily abolish the 

 entire complex by the destruction of one only of the component functional 

 connections. (See the summary by Dr. A. Meyer, 1910.) 



The general conclusion to be drawn from the entire series of 

 physiological and pathological studies of the cortex is that spe- 

 cific mental entities are not resident in particular cortical areas, 

 but that cortical functions involve the discharge of nervous en- 

 ergy from one or more sensory centers to various near and remote 

 regions, each of which, in turn, may serve as a point of departure 

 for new nervous discharges, and so on until the complexity of 

 action and interaction of part upon part becomes too intricate 

 for the mind to conceive. The resultant effect of all of these 

 nervous activities which reverberate from one association center 

 to another will be the establishment by a process of which we are 

 still in ignorance of an equilibrium, usually by means of a motor 

 discharge of some precise form from the cortex through the 

 pyramidal tract. 



This dynamic view of cortical function finds a further illustra- 

 tion in the realm of neuro-pathology in von Monakow's doctrine 

 of diaschisis. The onset of cerebral hemorrhage or any other 

 sudden injury to the cerebral cortex is usually marked by an 

 apoplectic "stroke," with profound shock and usually loss of 

 consciousness. The entire cortical equilibrium is disturbed and 

 this effect irradiates very widely throughout the nervous system. 

 If the injury is not too severe, there is soon a partial readjust- 

 ment of the nervous equilibrium and consciousness returns. But 

 the restoration is incomplete, for some of the normal factors 

 in the dynamic equilibrium complex are lacking by reason of the 

 destruction of the corresponding cortical areas or association 

 tracts. The intelligence is enfeebled and all voluntary control is 



