Please use this identifier to cite or link to this item: http://hdl.handle.net/2440/55033
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Type: Journal article
Title: Asymmetric activation of motor cortex controlling human anterior digastric muscles during speech and target-directed jaw movements
Author: Sowman, P.
Flavel, S.
McShane, C.
Sakuma, S.
Miles, T.
Nordstrom, M.
Citation: Journal of Neurophysiology, 2009; 102(1):159-166
Publisher: Amer Physiological Soc
Issue Date: 2009
ISSN: 0022-3077
1522-1598
Statement of
Responsibility: 
Paul F. Sowman, Stanley C. Flavel, Christie L. McShane, Shigemitsu Sakuma, Timothy S. Miles and Michael A. Nordstrom
Abstract: Like most of the cranial muscles involved in speech, the trigeminally innervated anterior digastric muscles are controlled by descending corticobulbar projections from the primary motor cortex (M1) of each hemisphere. We hypothesized that changes in corticobulbar M1 excitability during speech production would show a hemispheric asymmetry favoring the left side, which is the dominant hemisphere for language processing in most strongly right handed subjects. Fifteen volunteers aged 24.5 ± 5.3 (SD) yr participated. All subjects were strongly right handed as reported by questionnaire. A surface electromyograph (EMG) was recorded bilaterally from digastrics and jaw movement detected by an accelerometer attached to a lower incisor. Focal transcranial magnetic stimulation (TMS) was used to assess corticomotor excitability of the digastric representation in M1 of both hemispheres during four tasks: 1) static isometric contraction of digastrics; 2) speaking a single word; 3) visually guided, nonspeech jaw movement that matched the jaw kinematics recorded during task 2; and 4) reciting a sentence. Background EMG was well matched in all tasks and jaw kinematics were similar around the time of the TMS pulse for tasks 2–4. TMS resting thresholds and digastric muscle-evoked potential (MEP) size during isometric contraction did not differ for TMS over left versus right M1. MEPs elicited by TMS over left, but not right M1 increased in size during speech and nonspeech jaw movement compared with isometric contraction. We conclude that left corticobulbar M1 is preferentially engaged for descending control of digastric muscles during speech and the performance of a rapid jaw movement to match a target kinematic profile.
Keywords: Muscle, Skeletal; Jaw; Motor Cortex; Humans; Electromyography; Analysis of Variance; Electric Stimulation; Speech; Evoked Potentials, Motor; Action Potentials; Movement; Muscle Contraction; Adolescent; Adult; Female; Male; Transcranial Magnetic Stimulation; Functional Laterality; Young Adult
RMID: 0020090966
DOI: 10.1152/jn.90894.2008
Appears in Collections:Physiology publications

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