1718 IIWDBOOK OF PHYSIOLOGY >"> NEUROPHYSIOLOGY III 



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fig. 4. Localization of lesion in cases of sensory aphakia, 

 together with cases of nominal aphasia: 3 sensory aphasia; 

 O nominal aphasia. [From Conrad (27).] 



controversial (28, 43, 48, t;$8). As Hughlings Jackson 

 rightly observed, to localize a lesion provoking a 

 disorder of speech does not necessarily imply locali- 

 zation of speech itself. Further, the more recent trend 

 in experimental and clinical neurology is decidedly 

 against any rigid doctrine of cerebral localization of 

 psychological function. None the less, it is scarcely 

 open to doubt that the major central components of 

 linguistic activity involve more or less circumscribed 

 regions of the brain cortex and their subjacent con- 

 nections. The more strictly executive aspects of 

 language appear closely related to the left inferior 

 frontal cortex, although the critical region may well 

 extend beyond the traditional confines of Brora's area. 

 Word choice and syntax ben .1 special relation to the 

 temporoparietal cortex and appear closely bound up 

 with the auditory control of speech production. 

 Further, there is evidence that those aspects of 

 language chiefly dependent upon \ isuospatial orienta- 

 tion, e.g. reading, writing and some aspects of cal- 

 culation, are largely sustained by the posterior 

 parietal cortex (28, [14). Indeed, it has been argued 

 with some justice that the 'hub' of the essential 

 neural mechanisms subserving thought and speech is 

 to be sought in the temporoparietal region of the 

 dominant cerebral hemisphere (112). 



Induced Vocalization and Speet h Arrest 



Following earl) observations ol Foerstei 1 [8), 

 Penfield & Rasmussen (96, 97) have established that 

 both vocalization and transitory arrest of speech can 



fic. 5. Summary of areas in which stimulation mav interfere 

 with speech or produce vocalization in the dominant hemi- 

 sphere. [From Penfield & Rasmussen (97).] 



be induced in a conscious human subject by appro- 

 priate cortical stimulation produced bv either a 

 thyrotron or modified Ralmi stimulator As shown in 

 figure 5, vocalization may be elicited by stimuli 

 applied either to the precentral or postcentral gyrus, 

 more particularly the former. It takes the form of a 

 well-sustained vowel sound which cannot be arrested 

 by voluntary effort. Although the cry is evidently 

 primitive, its production involves complex innervation 

 of the abdominal muscles, larynx, pharynx and 

 tongue. But there is no coordinated alteration in 

 tongue and lip position or in expiratory control as 

 would be necessary lor articulate speech. Induced 

 vocalization is commonly, though not invariably, 

 .i-Mii i.ited with some involuntary lip or face move- 

 ment or, less frequently, with sensor) phenomena 

 referred to the mouth or face. The critical region for 

 induced vocalization appears to overlap the sensori- 

 motor representation of the lips, jaws and tongue. It 

 in. iv be induced with equal frequency from either 



hemisphere. 



Repetitive vocalization has been elicited in a small 

 number of cases bv stimulation within tin- longitudi- 

 nal fissure just anterior to the central fissure (14, (17 



This is described bv Penfield as superior frontal 

 v 1 icalization. 



Arrest of speech has been induced from all anas 



from which vocalization has been elicited. Speech 

 mav be slowed, rendered hesitant or completely 



