Single motor unit activity in levator veli palatini during speech and nonspeech tasks.

Abstract

This article assesses the control of velar movement by relating observed recruitment patterns of single motor unit activity in levator veli palatini observed during speech and nonspeech tasks in a single subject to intraoral pressure demands. Electromyographic activity was recorded from a single motor unit in levator veli palatini during repetitions of "Say (----) again" with selected consonant-vowel-consonant and consonant-vowel syllables, sustained high pressure consonants, and blowing tasks. Single motor unit firing characteristics (e.g., frequency of occurrence, firing frequency) were related to intraoral air pressures recorded during the sustained consonant and blowing tasks. Levator single motor unit activity was always present during the /s/ in "say" and the first and second /s/ in /sis/. Activity was observed less consistently during the production of the /s/ in /sus/, the /p/ in /p Lambda/, and the /g/ in "again." Single motor unit firing frequency ranged from 16.1 Hz to 22 Hz during phrase productions. Recruitment was observed during sustained productions of high-pressure consonants when intraoral pressures exceeded 15 cm H(2)O. Increases in intraoral air pressure were associated with 25% to 85% increases in single motor unit firing frequencies. During nonspeech blowing tasks, single motor unit activity was observed when intraoral air pressure exceeded approximately 12 cm H(2)O. Increases in intraoral air pressure were again associated with increased single motor unit firing rates. Results showed evidence of both preprogrammed and feedback-controlled responses by levator veli palatini to changes in task intraoral pressure demands.