i 7 it) 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 



quality of voice, shortened duration of phonation, 

 difficult) in enunciating vowels, and rapid vocal 

 fatigue. To this syndrome the name 'neurophonas- 

 thenia' has been given by Garde (40). 



Midbrain and Cerebellar Syndromes 



It has long been known that cerebellar lesions, if 

 extensive, are prone to produce defects of speech. 

 This may occur even when the lesion is unilateral, 

 more especially if the vermis is involved (56, 120). 

 The typical disorder consists in staccato or explosive 

 utterance, often with slurring dysarthria or undue 

 separation of syllables (scanning or syllabic speech). 

 It is usually ascribed to an asynergia of the many 

 muscles invoked in the act of speaking. This ma) 

 quite conceivably arise from failure to make proper 

 use of kinesthetic 'feedback' from the speech muscula- 

 ture, as has been argued in the parallel case of cere- 

 bellar dysmetria. 



A striking disorder of phonation, in some respects 

 unlike cerebellar dysarthria, has been described in 

 certain cases of head injury predominantly involving 

 the midbrain (70). Initially there may be complete 

 mutism, due perhaps to inability to coordinate 

 expiration with closure of the glottis and articulation. 

 With recovery, speech may pass through a stage of 

 forced and ill coordinated whispering before sounds 

 are produced. When voice is regained, it is commonly 

 high-pitched, monotonous and with marked lengthen- 

 ing of vowels quite unlike that ordinarily associated 

 with cerebellar disease. 1 1 has been argued by Husson 

 (6) ' that the rate, expressive intention and emotional 

 quality of speech are normally dependent upon 

 rhythmic discharges at the diencephalic level. 



Apraxu Dysarthria 



As is well known, any lesion within the pyramidal 

 system will, if bilateral, affect speech movements .is 

 part of the ensuing paralvsis, producing defect or 

 failure <>l articulation (dysarthria, anarthria). Uni- 

 lateral lesions, oil the Other hand, produce no per- 

 manent dysarthria and arlii -illation is not affected by 

 hemispherectomy (71 1. This is taken to imply that the 

 articulator} muscles are innervated from both 



hemispheres. A lesion within the motor cortex ol 

 either hemisphere mav, however, affect the move- 

 ments ol speaking as pat 1 ol a facial dyspraxia (apraxu 

 dysarthria). In this condition, there mav initially be 

 complete loss ol phonation; with recovery, vowel 



sounds are as a rule produced before consonants, 

 suggesting that tongue and lip movements are rela- 

 tively more dyspraxic than those of the larynx. As 

 with apraxia generally, emotional and reactive 

 expression is less affected than volitional speech. The 

 locus of the lesion provoking this syndrome has been 

 stated to be the lower part of the precentral gyrus 

 (89). Although the lenticular zone may be involved 

 to some extent, apraxic dysarthria would appear to be 

 essentially a syndrome of the motor cortex. According 

 to Nathan (89), it is to be envisaged as the highest 

 stage of dissolution of cortical motor function. 



Aphasia 



Whereas speech, physiologically considered, is a 

 pattern of movements, psychologically considered, it 

 is (he production of symbols serving in the expression 

 of thought (137). In the light of this distinction, it 

 has been customary to separate defects of articulation 

 from defects of language (aphasia 1. True, attempts 

 have been made to subsume motor aphasia to apraxia 

 and sensory aphasia to agnosia (81, 139), but these 

 formulations have failed to command general ac- 

 ceptance. For instance, the basic defect in eases of 

 motor aphasia can seldom, if ever, be wholly limited 

 to articulate speech. Thus written expression is 

 commonly as faulty and impoverished as oral speech 

 (138). The disorder would thus appear to transcend 

 mere asynergia or dyspraxia of the articulator 

 mechanism and to demand reference to the gram- 

 matical and syntactical categories of language. 

 Although aphasia may therefore be said to present 

 as a 'psychological' disorder, the modern treatment of 

 linguistic skills as essentially neurological offers hope 

 of escape from the bogy of the mind-body problem 

 and the limitations of traditional dualism (48, 1 p". 



Phonetii Disintegration in Aphasia 



An attempt has been made in recent vc.ns to apply 

 methods of experimental phonetics 10 the sindv of 

 aphasia (i, 2, J.5). In motor aphasia, emission of 

 phonemes is delayed and often explosive and there 

 mav be difficulty in passing from one phoneme to the 



next, e.g. from consonants 10 vowels. Tempo, cadence 



and modulation ol speech are uniformly abnormal 

 It has therefore been inferred that paretic, dystonic 

 and dyspraxic elements constitute the pattern of 

 'phonetic disintegration.' from the phonetic stand- 

 point, it is interesting to note that no obvious differ- 



