PRACTICAL CONSIDERATIONS : THE BRAIN. 



1213 



In Broca's convolution is probably the centre for motor speech, and a lesion 

 here gives motor aphasia, an inability to transform concepts into words, although 

 the patient is conscious and the tongue can be moved. A minor part in speech is 

 played by the posterior part of the right third frontal convolution, but in the left- 

 handed it is probably the chief centre. 



In the first left temporal convolution is the auditory centre for speech, a lesion 

 of which leads to a loss of memory for word-sounds, though the hearing may be 

 undisturbed. 



The centre for memory of printed words is probably in the left angular gyrus ; 

 and a lesion there probably causes a loss of the ability to read or to understand 

 written language, though ordinary sight is undisturbed. The existence of a motor 

 writing centre is doubtful (Oppenheim). If it exists, it is probably located in the 

 posterior portion of the left second frontal convolution. 



We have no definite knowledge of the location of centres for smell and taste. 

 That for smell is thought to lie in the uncinate gyrus. The centre for taste has been 

 supposed to be in the anterior portion of the gyrus fornicatus, but it is not decided, 

 although it is probably near the centre for smell. 



FIG. 1043. 



Diagram illustrating probable relations of physiological areas and centres of mesial aspect of right cerebral 



hemisphere. (Mills.) 



The auditory centre, as indicated, is in the upper temporal convolution. It is 

 very likely that the centre of each side is connected with both auditory nerves, so 

 that a paralysis of one side by a unilateral lesion of one side m'ay be compensated for 

 by the centre of the opposite side. 



It is probable that no part of the cerebral cortex is absolutely without function, 

 although the functions of some areas are very little known. Unilateral disease of the 

 anterior portion of the frontal lobe may be extensive without notable symptoms of any 

 kind. The atrophy is often most marked here in general paralysis of the insane, 

 and in other forms of dementia. It is generally agreed that the seat of " the higher 

 psychical functions ' ' is located in the prefrontal lobes, the left side being perhaps 

 more active than in the right. 



Reference has already been made to the relation of the occipital cortex to sight, 

 and of the temporal to hearing. The cuneus and calcarine fissure together constitute 

 a primary or lower cortical or visuo-sensory centre, while the lateral aspect of the 

 occipital lobe is a visuo-psychic area, containing sub-areas or centres concerned with 

 higher visual processes. Mind blindness, for instance, results from destructive lesion 

 of the lateral occipital lobe, particularly if the lesion is a large one, in the left hemi- 

 sphere, or if lesions of both occipital lobes are present. A lesion of the cuneo- 

 calcarine cortex causes lateral homonymous hemianopsia. This may be produced 



