Evidence for speech muscle functional compartmentalization: Theoretical and methodological implications

Abstract

An assumption underlying most studies using speech electromyography is that classifically defined muscles, as anatomical entities, are functionally singular in their actions. Contrary to this assumption are recent findings in humans and animals suggesting consistent functional subdivisions of anatomically distinct limb muscles with movement‐related specialization of the subdivisions and differential activation from supraspinal sites and/or peripheral afferents. To evaluate this organization in the speech muscles, 3–5 electrodes with restricted pickup fields (i.e., two wires/needle) were placed in the Orbicularis Oris Inferior and muscle activity was observed for actions involving labial occlusion, elevation, and protrusion, all of which have been observed previously to involve some OOI activity. Speech tasks also were manipulated to create variations in the velocity of elevation and protrusion movement. Consistent temporal and spatial variations were observed from the multiple electrode sites suggesting functional subdivisions similar to those observed in the limb muscles. Results will be discussed in relation to organization of complex speech motor gestures and methodological implications, particularly EMG recording with restricted field electrodes. [Research supported by NINCDS Grant.]