Single motor unit activity in the genioglossus muscle during vowel articulation

There is an abundance of previous electromyographic (EMG) research conducted in the human tongue that has as its focus the extrinsic tongue muscle, genioglossus (GG) and its role in preserving upper airway patency for purposes of gas exchange. Comparatively few studies have documented GG EMG activities in the performance of volitional tasks such as speech production (Honda 1992; Honda et al. 1992; Kusakawa et al 1993). Here we report on de novo efforts to characterize GG single motor unit (SMU) activities in the context of volitional i.e., speech and automatic i.e., central pattern generator driven respiratory activities. Using tungsten microelectrodes inserted into the belly of the GG in 5 healthy adults, we recorded SMU activity during static articulation of the vowels [a] and [ae] in three conditions: phonated, whispered, and articulation using an electrolarynx. Preliminary findings provide evidence of recruitment and de-recruitment of GG motor units coincident with the onset and offset of vowel articulation in phonated and whispered, but not electrolarynx conditions. Furthermore, fluctuations in GG MU firing rates mirror intensity variations within phonated and whispered utterances. These findings provide much-needed new insights into the differential modulation of lingual motor unit activities for purposes of speech production versus breathing.