vill] /'iiffctdl Area '20-> 



A CONSIDERATION OF THE FUNCTION OK THE PARIETAL AREA. 



Stimulation experiments supply negative information only concerning the function of the 

 parietal cortex. According to those physiologists from whose observations our original plans 

 of the surface localisation of the motor function were drawn, the excitable area extends 

 backwards on to the superior parietal gyms, and therefore into the histological field forming 

 the subject of these remarks; but in the chapters on the " precentral " and " postcentral" 

 areas the accuracy of this localisation has been called in question and contradicted, and in 

 my opinion it may now be taken as proved that the area enveloped by a "parietal" type 

 of cortex forms a part of the extensive territory distinguished by its "silence" under the 

 influence of special electrical stimulation. 



As to the information forthcoming from a study of experimentally-produced secondary 

 ill 'generations, this also is not enlightening. The chief question which has claimed attention 

 is, whether or not the parietal lobe is the end-station for the cortical lemniscus, and, as has 

 been mentioned in the discussion on the functions of the " posteentral " area, the evidence 

 on this point is contradictory, von Monakow answering the question in the affirmative, while 

 Tschermak writes to the contrary. Which of the two is correct it is impossible to say defi- 

 nitely, but I have already given many reasons for believing, along with Tschermak, that the 

 postcentral gyrus, and not the parietal lobe, is the main sensory goal ; still, a certain structural 

 resemblance between the " parietal " and the " postcentral " cortex and other evidence, chiefly 

 clinical and to be presently mentioned, stand in von Monakow's support and make it appear 

 that at any rate some centripetal sensor} 7 fibres gain the cortex of the " parietal " area, even 

 though the mass makes for the postcentral gyrus. 



Let us take next the information derived from a study of the clinical effects of lesions 

 in the ' parietal " area. The records contain several instructive reports of such cases, and, 

 as I have previously stated (postcentral area), if these be analysed, a consensus of opinion 

 will be noticed to the effect that damage to this part of the brain is attended by disorder 

 of high and combined forms of sensation, such as the muscle sense and that of stereognosis 

 (Durante, Walton and Paul, von Monakow, Redlich and many others). Analysed more closely, 

 we find that if the lesion be in the precuneus, or in the superior parietal gyrus, the sensory 

 impairment will be confined to the lower extremity (observations of Bernhardt, Westphal, 

 Henschen, etc.), and if, on the other hand, the supramarginal gyrus be destroyed the affection 

 will be restricted to the upper extremity (cases of von Monakow, Vetter, etc.). For the 

 clinician, therefore, the field which I have mapped out and called "parietal" represents a 

 high sensory centre, a centre for the recognition of complex impressions embodied in the 

 muscle sense and that of stereognosis. And this is a view which, after my histological 

 investigations, I should have least compunction in endorsing. For although it has been upheld 

 in a previous chapter that the cortex of the area designated " intermediate postcentral " is 

 chiefly constituted for the elaboration of sensory psychic attributes, it has also been conceded 

 that this function might be shared by cortex situated further back in the parietal lobe, 

 and the part to which I referred in making that concession was the special " parietal " field 

 now under discussion. And my principal reason for that statement was the histological know- 

 ledge that the cortex of this particular area had a distinct resemblance to that of the 

 " intermediate postcentral," it differs only in point of degree of representation of certain 

 elements, now also it may be understood why I was diffident in giving this area 

 independence. 



