The effects of deep-reaching lesions in the cortical face area on phonation. A combined case report and experimental monkey study.

The present study compares the phonatory ability of a patient with a deep-reaching left-sided lesion in the region of the cortical face area with that of two squirrel monkeys in which the patient's lesion has been reduplicated bilaterally. The lesion involved Broca's area, the inferior pre- and postcentral cortex, rolandic operculum, inferior parietal cortex insula, claustrum, parts of the putamen and white matter underlying the inferior frontoparietal and insular cortex. While the squirrel monkey did not show any phonatory deficits, the patient became aphonic for more than 10 weeks following the insult. After that period, phonation recovered steadily to a slightly breathy but monotonous voice with a somewhat reduced singing capacity. During the aphonic period, there was a bilateral complete paresis of the vocal folds. Both, patient and monkey, showed a paresis of the lower facial and tongue muscles which was accompanied by dysarthria and buccolingual apraxia in the patient and feeding difficulties in the monkey. The discrepancy between human aphonia and intact monkey phonation, on the one hand, and intact phonation and defective orofacial behaviour in the monkey, on the other, is explained by the anatomical fact that there is a direct cortical projection to the nucleus ambiguus in man but not in monkey, whereas the facial and hypoglossal nuclei receive direct cortical projections in man and monkey. The lack of direct cortical control of the laryngeal motoneurones in the monkey is paralleled by a lack of volitional control of fine vocal fold movements.