Activation of Lip Motor Units With Variations in Speech Rate and Phonetic Structure

1995 ◽  
Vol 38 (4) ◽  
pp. 772-782 ◽  
Author(s):  
Michael D. McClean ◽  
John L. Clay
Keyword(s):  
Speech Rate ◽  
Motor Units ◽  
Interspike Intervals ◽  
Single Motor Unit ◽  
Lower Lip ◽  
Firing Rates ◽  
Single Motor ◽  
Single Motor Units ◽  
Lip Movement ◽  
Intraoral Pressure

The purpose of this study was to describe the activation characteristics of lip-muscle single motor units in relation to speech rate and phonetic structure. Repeated experiments were carried out on three adult subjects from whom recordings of lower lip EMG and two-dimensional displacement were obtained. Single motor unit recordings were obtained from the orbicularis oris inferior (OOI), depressor labii inferior (DLI), and mentalis (MENT) muscles. Subjects' tasks involved repeating CV syllables at 1 to 4 syllables per second (syl/sec). The distribution of interspike intervals and corresponding firing rates were obtained on 11 motor units. The firing rates of OOI and MENT motor units increased as syllable rate changed from 1 to 3 syl/sec, but firing rates tended to be equivalent at 3 and 4 syl/sec. DLI and tonic motor units showed little or no modulation in their firing rates with speech rate. Firing rate data and related observations on lip movement and EMG spike count levels suggest that distinct neuromechanical processes control lip movements at low and high speech rates. Both kinematic and EMG data support the expectation that phonetic structure has its greatest effects on lip opening compared to lip closing movements in CV syllables. OOI and MENT activation levels tended to be highest for /p/ productions compared to /w/ and /f/. This may be related to the requirements for complete lip closure and elevated levels of intraoral pressure for production of /p/.

Rectification is required to extract oscillatory envelope modulation from surface electromyographic signals

2014 ◽  
Vol 112 (7) ◽  
pp. 1685-1691 ◽  
Author(s):  
Christopher J. Dakin ◽  
Brian H. Dalton ◽  
Billy L. Luu ◽  
Jean-Sébastien Blouin
Keyword(s):  
Motor Unit ◽  
Stimulus Frequency ◽  
Motor Units ◽  
Surface Emg ◽  
Medial Gastrocnemius ◽  
Single Motor Unit ◽  
Single Motor ◽  
Single Motor Units ◽  
Emg Signal ◽  
Envelope Modulation

Rectification of surface electromyographic (EMG) recordings prior to their correlation with other signals is a widely used form of preprocessing. Recently this practice has come into question, elevating the subject of EMG rectification to a topic of much debate. Proponents for rectifying suggest it accentuates the EMG spike timing information, whereas opponents indicate it is unnecessary and its nonlinear distortion of data is potentially destructive. Here we examine the necessity of rectification on the extraction of muscle responses, but for the first time using a known oscillatory input to the muscle in the form of electrical vestibular stimulation. Participants were exposed to sinusoidal vestibular stimuli while surface and intramuscular EMG were recorded from the left medial gastrocnemius. We compared the unrectified and rectified surface EMG to single motor units to determine which method best identified stimulus-EMG coherence and phase at the single-motor unit level. Surface EMG modulation at the stimulus frequency was obvious in the unrectified surface EMG. However, this modulation was not identified by the fast Fourier transform, and therefore stimulus coherence with the unrectified EMG signal failed to capture this covariance. Both the rectified surface EMG and single motor units displayed significant coherence over the entire stimulus bandwidth (1–20 Hz). Furthermore, the stimulus-phase relationship for the rectified EMG and motor units shared a moderate correlation ( r = 0.56). These data indicate that rectification of surface EMG is a necessary step to extract EMG envelope modulation due to motor unit entrainment to a known stimulus.

Functional Properties of Single Motor Units in the Inferior Head of Human Lateral Pterygoid Muscle: Task Firing Rates

2002 ◽  
Vol 88 (2) ◽  
pp. 751-760 ◽  
Author(s):  
I. Phanachet ◽  
T. Whittle ◽  
K. Wanigaratne ◽  
G. M. Murray
Keyword(s):  
Firing Rate ◽  
Correlation Coefficients ◽  
Motor Units ◽  
Lateral Pterygoid Muscle ◽  
Jaw Movements ◽  
Firing Rates ◽  
Single Motor ◽  
Single Motor Units ◽  
Fine Control ◽  
Contralateral Movement

The precise function of the inferior head of the human lateral pterygoid muscle (IHLP) is unclear. The aim of this study was to clarify the normal function of the IHLP. The hypothesis was that an important function of the IHLP is the generation and fine control of horizontal (i.e., anteroposterior and mediolateral) jaw movements. The activities of 50 single motor units (SMUs) were recorded from IHLP (14 subjects) during two- or three-step contralateral movement ( n = 36) and/or protrusion ( n = 33). Most recording sites were identified by computer tomography. There was a statistically significant overall increase in firing rate as the magnitude of jaw displacement increased between the holding phases (range of increments: 0.3–1.6 mm). The firing rates during the dynamic phases for each unit were significantly greater than those during the previous holding phases but less than those during the subsequent holding phases. For the contralateral step task at the intermediate rate, the cross-correlation coefficients between jaw displacement in the mediolateral axis and the mean firing rate of each unit ranged from r = 0.29 to 0.77; mean ± SD; r = 0.49 ± 0.13 (protrusive step task: r = 0.12–0.74, r = 0.44 ± 0.14 for correlation with anterior–posterior axis). The correlation coefficients at the fast rate during the contralateral step task and the protrusive step task were significantly higher than those at the slow rate. The firing rate change of the SMUs per unit displacement between holding phases was significantly greater for the lower-threshold than for the higher-threshold units during contralateral movement and protrusion. After dividing IHLP into four regions, the SMUs recorded in the superior part exhibited significantly greater mean firing rate changes per unit displacement during protrusion than for the SMUs recorded in the inferior part. Significantly fewer units were related to the protrusive task in the superior–medial part. These data support previously proposed notions of functional heterogeneity within IHLP. The present findings provide further evidence for an involvement of the IHLP in the generation and fine control of horizontal jaw movements.

Comparison of the contractile responses to irregular and regular trains of stimuli during microstimulation of single human motor axons

2014 ◽  
Vol 111 (7) ◽  
pp. 1499-1506 ◽  
Author(s):  
Michael Leitch ◽  
Vaughan G. Macefield
Keyword(s):  
Angular Displacement ◽  
Motor Units ◽  
Common Peroneal Nerve ◽  
Displacement Transducer ◽  
Motor Axons ◽  
Interspike Intervals ◽  
Contractile Responses ◽  
Single Motor ◽  
Single Motor Units ◽  
Voluntary Contractions

During voluntary contractions, human motoneurons discharge with a physiological variability of ∼20%. However, studies that have measured the contractile responses to microstimulation of single motor axons have used regular trains of stimuli with no variability. We tested the hypothesis that irregular (physiological) trains of stimuli produce greater contractile responses than regular (nonphysiological) trains of identical mean frequency but zero variability. High-impedance tungsten microelectrodes were inserted into the common peroneal nerve and guided into fascicles supplying a toe extensor muscle. Selective microstimulation was achieved for 14 single motor axons. Contractile responses were measured via an angular displacement transducer over the relevant toe. After the responses to regular trains of 10 stimuli extending from 2 to 100 Hz were recorded, irregular trains of 10 stimuli, based on the interspike intervals recorded from single motor units during voluntary contractions, were delivered. Finally, the stimulation sequences were repeated following a 2-min period of continuous stimulation at 10 Hz to induce muscle fatigue. Regular trains of stimuli generated a sigmoidal increase in displacement with frequency, whereas irregular trains, emulating the firing of volitionally driven motoneurons, displayed significantly greater responses over the same frequency range (8–24 Hz). This was maintained even in the presence of fatigue. We conclude that physiological discharge variability, which incorporates short and long interspike intervals, offers an advantage to the neuromuscular system by allowing motor units to operate on a higher level of the contraction-frequency curve and taking advantage of catch-like properties in skeletal muscle.

Organization of single motor units in feline sartorius

1994 ◽  
Vol 72 (4) ◽  
pp. 1885-1896 ◽  
Author(s):  
E. Smits ◽  
P. K. Rose ◽  
T. Gordon ◽  
F. J. Richmond
Keyword(s):  
Motor Unit ◽  
Cross Section ◽  
Cross Sections ◽  
Muscle Fibers ◽  
Motor Units ◽  
Single Motor Unit ◽  
Single Motor ◽  
Medial Head ◽  
Single Motor Units ◽  
Fast Twitch

1. We depleted single motor units in feline sartorius muscles of glycogen by stimulating their motoneurons intracellularly. We mapped the intramuscular distribution of depleted fibers by inspecting histological cross-sections throughout the length of sartorius. 2. We selected ten depleted motor units for detailed study and quantitative analysis. Nine motor units were located in the anterior head of sartorius. One was located in a muscle whose distal half appeared to have been damaged some time before the acute experiment. A single motor unit was located in the medial head of sartorius. 3. Five motor units were composed of fast-twitch glycolytic (FG) muscle fibers, two of fast-twitch oxidative glycolytic (FOG) muscle fibers, and three of slow-twitch oxidative (SO) muscle fibers. Estimates of the numbers of depleted fibers in motor units of anterior sartorius indicated that FG motor units were larger (mean 566 fibers) than FOG and SO motor units (SO mean 190, FOG mean 156 fibers). The SO motor unit in the damaged muscle had 550 fibers. One motor unit depleted in the medial head of sartorius had 270 fibers with FG profiles. 4. Muscle fibers belonging to each anterior motor unit were never distributed throughout the whole cross-section of anterior sartorius at any proximodistal level. Furthermore, fibers were distributed nonuniformly along the proximodistal axis of the muscle. In most muscles at least a few depleted fibers were found at all proximodistal levels. However, in one normal muscle and the damaged muscle, depleted fibers were confined to the proximal end. 5. The fibers in the medial motor unit were confined to a strip that did not extend across the whole cross-section of the muscle head. Fibers within this strip were scattered quite evenly from origin to insertion. This medial FG motor unit occupied a smaller territory and contained fewer fibers than anterior motor units of the same histochemical type. 6. These results show that sartorius motor units are not distributed uniformly in the mediolateral plane; those in anterior sartorius were distributed asymmetrically in the proximodistal axis as well. This finding has important functional implications for the way in which we model force development and transmission in sartorius and other long muscles.

Fatigue of single motor units in human masseter

1990 ◽  
Vol 68 (1) ◽  
pp. 26-34 ◽  
Author(s):  
M. A. Nordstrom ◽  
T. S. Miles
Keyword(s):  
Time Course ◽  
Motor Units ◽  
Medial Gastrocnemius ◽  
Type I ◽  
Single Motor Unit ◽  
Single Motor ◽  
Single Motor Units ◽  
Spike Triggered Averaging ◽  
Human Fatigue ◽  
Type I Fibers

The spike-triggered averaging technique was used to determine the time course and extent of fatigue of single motor unit twitches in the human masseter. This is the first report of a fatigue test having been applied to masseter motor units in either animals or humans. The human masseter was found to be comprised predominantly of fast-twitch motor units with a broad spectrum of fatigability. Very few physiological type S units were found, despite histochemical evidence for a substantial population of type I fibers in the masseter. In addition, there was no significant correlation between fatigability and either twitch amplitude or contractile speed in the motor units studied. The latter observations are consistent with the unusual histological features of the masseter. Comparison with other human fatigue data suggests that the extent of fatigue in the present population of masseter motor units after approximately 3,000 activations is similar to that reported for populations of units in first dorsal interosseous and medial gastrocnemius.

Discharge Characteristics of Laryngeal Single Motor Units During Phonation in Young and Older Adults and in Persons With Parkinson Disease

1999 ◽  
Vol 81 (5) ◽  
pp. 2131-2139 ◽  
Author(s):  
Erich S. Luschei ◽  
Lorraine O. Ramig ◽  
Kristin L. Baker ◽  
Marshall E. Smith
Keyword(s):  
Older Adults ◽  
Parkinson Disease ◽  
Skeletal Muscles ◽  
Motor Units ◽  
Discharge Characteristics ◽  
Laryngeal Muscles ◽  
Firing Rates ◽  
Single Motor ◽  
Single Motor Units ◽  
Human Skeletal Muscles

Discharge characteristics of laryngeal single motor units during phonation in young and older adults, and in persons with Parkinson disease. The rate and variability of the firing of single motor units in the laryngeal muscles of young and older nondisordered humans and people with idiopathic Parkinson disease (IPD) were determined during steady phonation and other laryngeal behaviors. Typical firing rates during phonation were ∼24 s/s. The highest rate observed, during a cough, was 50 s/s. Decreases in the rate and increases in the variability of motor unit firing were observed in the thyroarytenoid muscle of older and IPD male subjects but not female subjects. These gender-specific age-related changes may relate to differential effects of aging on the male and female voice characteristics. The range and typical firing rates of laryngeal motor units were similar to those reported for other human skeletal muscles, so we conclude that human laryngeal muscles are probably no faster, in terms of their contraction speed, than other human skeletal muscles. Interspike interval (ISI) variability during steady phonation was quite low, however, with average CV of ∼10%, with a range of 5 to 30%. These values appear to be lower than typical values of the CV of firing reported in three studies of limb muscles of humans. We suggest therefore that low ISI variability is a special although not unique property of laryngeal muscles compared with other muscles of the body. This conceivably could be the result of less synaptic “noise” in the laryngeal motoneurons, perhaps as a result of suppression of local reflex inputs to these motoneurons during phonation.

Single motor unit activity in the diaphragm of cat during pressure breathing

1981 ◽  
Vol 50 (2) ◽  
pp. 348-357 ◽  
Author(s):  
B. Bishop ◽  
S. Settle ◽  
J. Hirsch
Keyword(s):  
Motor Unit ◽  
Negative Pressure ◽  
Motor Units ◽  
Positive Pressure ◽  
Quiet Breathing ◽  
Single Motor Unit ◽  
Single Motor ◽  
Single Motor Units ◽  
Negative Pressure Breathing ◽  
Phrenic Motoneuron

In this study we analyzed the breath-by-breath activity of single motor units in the diaphragm slip of allobarbital-anesthetized cats during quiet breathing and during continuous positive- and negative-pressure breathing. Our objective was to determine whether single motor units, on the basis of their activities, can be separated into discrete subpopulations or whether they fall on a continuum analogous to that of motor units of hindlimb muscles. The firing profiles of each unit were characterized for each pressure level by the onset and peak firing frequencies, onset latency, duration of firing, number of impulses per breath, and minimal frequency, when appropriate. Units with shorter onset latencies had higher peak frequencies, longer firing durations, and increased firing frequencies than did units with longer onset latencies. These comparative relationships persisted even though the activity of every motor unit was altered during pressure breathing. During positive-pressure breathing onset latencies were lengthened, and durations of firing were shortened with little change in onset or peak frequencies. Late units might be silenced. During negative-pressure breathing onset latencies were shortened, and durations of firing were lengthened, sufficiently in some cases to fill the expiratory pause. In addition, previously inactive units were recruited late in inspiration for short, relatively high frequency bursts during inspiration. The results support the concept that the phrenic motoneuron pool is comprised of three discrete subpopulations.

scholarly journals Discharge frequencies of single motor units in human diaphragm and parasternal muscles in lying and standing

2001 ◽  
Vol 90 (1) ◽  
pp. 147-154 ◽  
Author(s):  
J. E. Butler ◽  
D. K. McKenzie ◽  
S. C. Gandevia
Keyword(s):  
Tidal Volume ◽  
Motor Unit ◽  
Motor Units ◽  
Neural Drive ◽  
Unit Discharge ◽  
Single Motor Unit ◽  
Single Motor ◽  
Single Motor Units ◽  
Inspiratory Muscles ◽  
Motor Unit Discharge

Single motor unit discharge was measured directly in diaphragm and parasternal intercostal muscles to determine whether neural drive to human inspiratory muscles changes between lying and standing. The final discharge frequency of diaphragmatic motor units increased slightly, by 1 Hz (12%; P < 0.01), when subjects were standing [182 units, median 9.1 Hz (interquartile range 7.6–11.3 Hz)] compared with lying supine [159 units, 8.1 Hz (6.6–10.3 Hz)]. However, this increase with standing occurred in only two of six subjects, in one of whom tidal volume increased significantly during standing. Parasternal intercostal motor unit final discharge frequencies did not differ between standing [116 units, 8.0 Hz (6.6–9.6 Hz)] and lying [124 units, 8.4 Hz (7.0–10.3 Hz)]. The discharge frequencies at the onset of inspiration did not differ between lying and standing for either muscle. A larger proportion of motor units in both inspiratory muscles had postinspiratory or tonic expiratory activity for lying compared with standing (15 vs. 4%; P < 0.05). We conclude that there is no major difference in the phasic inspiratory drive to the diaphragm with the change in posture.

Reduced motor unit activation of muscle spindles and tendon organs in the immobilized cat hindlimb

1995 ◽  
Vol 78 (3) ◽  
pp. 901-913 ◽  
Author(s):  
M. A. Nordstrom ◽  
R. M. Enoka ◽  
R. M. Reinking ◽  
R. C. Callister ◽  
D. G. Stuart
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Muscle Spindles ◽  
Tibialis Posterior ◽  
Fiber Types ◽  
Single Motor Unit ◽  
Tetanic Force ◽  
Single Motor ◽  
Single Motor Units ◽  
Tendon Organs

Six weeks of limb immobilization of a healthy muscle (cat tibialis posterior) at a short length resulted in a significant reduction of mean fiber area for all fiber types (I, 71% of control; IIa, 77% of control; IIb, 79% of control), whereas fiber type proportions were unchanged. For motor units, there was a reduction in peak tetanic force (type slow > fast fatigue resistant > fast fatigable); an increase in the twitch-to-tetanus ratio for fast fatigue-resistant and slow units; and no effect on the twitch force, twitch time course, or fatigability. The reduction in peak force was greater than expected because of fiber atrophy in slow units. Immobilization had a minimal effect on muscle spindle afferent (Ia and spindle group II) responses to a ramp-and-hold stretch of the passive muscle. Tendon organ (Ib) afferents had an increased responsiveness to stretch after immobilization but only when the muscle was stretched from a short resting length. However, immobilization reduced the modulation of muscle afferent discharge in response to tetanic contractions of single motor units. The decline in responsiveness of spindles was a result of the reduced tetanic force of motor units. In contrast, tendon organs in immobilized muscle were twice as likely to convey no information on the contraction of a single motor unit and were more likely to be unloaded, suggesting that immobilization caused the functional denervation of some muscle fibers. Thus the responses of muscle spindles and tendon organs in immobilized muscle reflected atrophic changes in extrafusal fibers but did not provide evidence for substantial disturbance of receptor function.

Changes in Voice Fundamental Frequency Following Discharge of Single Motor Units in Cricothyroid and Thyroarytenoid Muscles

1987 ◽  
Vol 30 (4) ◽  
pp. 552-558 ◽  
Author(s):  
Charles R. Larson ◽  
Gail B. Kempster ◽  
Michael K. Kistler
Keyword(s):  
Motor Unit ◽  
Averaging Method ◽  
Motor Units ◽  
Vocal Folds ◽  
Single Motor Unit ◽  
Single Motor ◽  
Cricothyroid Muscle ◽  
Single Motor Units ◽  
Contraction Times ◽  
Voice Fundamental Frequency

This investigation was designed to measure voice F 0 changes related to single motor unit (SMU) contractions in the cricothyroid and thyroarytenoid muscles. Four subjects (3 men and 1 woman) were recorded producing a prolonged vowel at modal pitch and loudness levels while simultaneous recordings of electromyograms (EMG) from the muscles were obtained. Voice F 0 changes unrelated to SMU firings in the muscles were eliminated using an averaging method previously described by Baer (1979). Results indicate that the time between discharge of the SMU and the peak in F 0 Change ("F 0 Latency") was variable and ranged from 5 to 20 ms for the thyroarytenoid and 6 to 75 ms for the cricothyroid muscle. Distinct oscillations in F 0 were always present in recordings from the woman subject and from the men when they phonated at higher-than-modal pitch levels. The findings are discussed in relation to SMU contraction times, biomechanics of the vocal folds, and the presence of jitter in normal voices.

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