The role of the left mesial frontal cortex in fluent speech: Evidence from a case of left supplementary motor area hemorrhage

Abstract

This study reports on a woman who suffered left anterior cerebral artery hemorrhage with a focal lesion undercutting the left supplementary motor area. After almost complete recovery of language the patient was left with dysfluent, halting speech. In a series of four experiments we examined the major factors influencing the patient's articulation. There was a significant effect of lexicality and syllabic length on repetition and articulatory learning (Experiments 1 and 2). The number of syllables was also found to influence, in a simple reaction task, onset latencies, but not inter-response times (Experiment 3). On the contrary, articulatory intricacy had no particular effect on either repetition or vocal reaction (Experiments 1 and 3). While repetition of real words was preserved, single word production in word generation tasks was impaired. Rhyme generation and alliteration. both of which rely on phonological processing, were particularly involved, whereas semantic word generation tasks like verb generation and generation of category members were relatively spared (Experiment 4). Control tasks revealed that the observed phonological processing deficit was confined to the condition of generating spoken language output. These experimental findings suggest that the patient's dysfluent speech could neither be attributed to a deficit of linguistic processing proper, nor to one of motor execution. Her speech disorder rather resulted from an impairment of initiating sequential articulations, particularly in association with the process of downloading temporarily stored multisyllabic strings from an articulatory buffer. This deficit could obviously be overcome in real word repetition through the use of a semantic lexical route.