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Y Masakado

Publications and source records attributed to Y Masakado.

12 recordsLinked to original sources
PubMed2001

Synchronization of single motor units during voluntary contractions in the upper and lower extremities.

OBJECTIVE: To investigate motor unit synchronization in the time and frequency domains and compare the amount and nature of this synchronization between upper and lower extremity muscles in human subjects. METHODS: A total of 120 motor unit pairs from biceps brachii (BB), first dorsal interosseous (1DI), vastus medialis (VM), and tibialis anterior (TA) on the dominant side were analyzed and compared. Pairs of motor unit spike trains were recorded from two concentric needle electrodes inserted within these muscles in healthy volunteers. Subjects were instructed to maintain a weak isometric contraction of these muscles so that an individual motor unit recorded from each concentric needle discharged at a steady rate of approximately 10 impulses/s. Pairs of motor unit spike trains were cross-correlated in the time domain, and coherence analysis in the frequency domain was performed on the same spike train data. RESULTS: Synchronization was seen in all the muscles studied. Strength of motor unit synchronization, expressed as synchronization index (SI), was greater in 1DI muscles compared to other muscles (P<0.01). Coherence analysis revealed significant association between motor unit firings in the 1--5 and 25--30 Hz frequency ranges in all the muscles studied. The incidence of 25--30 Hz coherence peaks were found to be greater for 1DI muscles compared to other muscles. CONCLUSION: The above results suggest a possible role for corticospinal projections in producing pre-synaptic inputs responsible for synchronization of motor unit firings and 25--30 Hz coherence peaks.

Action Potentials↗
PubMed2000

Quantitative EMG and motor unit recruitment threshold using a concentric needle with quadrifilar electrode.

According to Henneman's size principle, small motor units are recruited before large ones. We used the electromyographic (EMG) signal decomposition technique to determine the quantitative relationships between five motor unit action potential (MUAP) parameters (amplitude, duration, area, thickness, and size index) and the recruitment threshold of the motor units recruited up to 50% of the maximum voluntary contraction in the first dorsal interosseous, biceps brachii, rectus femoris, and tibialis anterior muscles of 5 healthy young men. In each muscle, the amplitude, duration, area, and size index had significant, positive high correlations with the motor unit recruitment thresholds. We conclude that the size principle applies to recordings made with concentric needle EMG electrodes under special recording conditions, and therefore that more importance should be attached to the patient's contraction force during EMG examinations in order to evaluate MUAPs for electrodiagnostic purposes.

Adult↗
PubMed2000

Tonic and kinetic motor units revisited: does motor unit firing behavior differentiate motor units?

OBJECTIVE: We tried to differentiate motor unit into two distinct populations, tonic and kinetic, on the basis of the relationship between the mean inter-spike interval and its variability. METHODS: During voluntary isometric contraction myoelectric activity was recorded with a special quadrifilar electrode from first dorsal interosseous, biceps brachii, soleus, and tibialis anterior muscle. Motor unit action potentials (MUAP) were decomposed into individual MUAP trains, by electromyography (EMG) signal decomposition. The variability in the instantaneous firing rate was assessed at two or more levels of contraction in each muscle. RESULTS: We found each muscle tested had a homogeneous population. There were no tonic and kinetic motor units. But there were differences in the variability in the instantaneous firing rate in the 4 muscles tested. CONCLUSION: Motor unit firing behavior in a muscle may be fitted for its function.

Action Potentials↗
PubMed2000

Physiologic decrease of single thenar motor units in the F-response in stroke patients.

OBJECTIVE: To investigate the left-right difference and the reproducibility by the F-wave motor unit number estimation and to compare the motor unit number between the hemiplegic and unaffected side in stroke patients. SETTING: A referral center and institutional practice providing outpatient care. SUBJECTS: Seven healthy volunteers and 15 consecutive stroke patients. DESIGN: Diagnostic statistical test and correlational study. METHOD: Submaximal stimuli were used to evoke a sample of surface motor unit action potentials (S-MUAPs) in the F-waves that are entirely representative of the relative numbers of detected S-MUAPs of different sizes. The average S-MUAP amplitude was calculated from a selected population of F-wave responses for each abductor pollicis brevis (APB) muscle. The motor unit number was calculated by dividing the maximum M-potential negative peak amplitude by the average S-MUAP negative peak amplitude. RESULT: There was no statistical difference between motor unit numbers on either side and between test and retest in this motor unit number estimation method among normal subjects. The motor unit number on the hemiplegic side was significantly lower than on the unaffected side (p < .05, Mann-Whitney test) among stroke patients. CONCLUSION: The motor unit could decrease in the hemiplegic side after a moderate-to-severe hemiplegic stroke and this decrement might be due to the transsynaptic degeneration secondary to an upper motor neuron lesion.

Action Potentials↗
PubMed2000

Rise time or rise rate: which should be a criterion for analysing motor unit action potentials?

We measured the rise time (RT) and rise rate (RR) of motor unit action potentials (MUAPs) when sharp sounds are heard in concentric EMG in the first dorsal interosseus muscle (FDI) and biceps brachii muscle (BIC) of normal subjects. MUAPs from FDI muscle with an RT of less than 500 microseconds were 85%, and those of more than 500 microseconds were 15%. In contrast, MUAPs from BIC muscle with an RT of less than 500 microseconds were 65%, and those of more than 500 microseconds were 35%. Distributions of the RR for FDI and BIC were also determined. MUAPs from FDI muscle with an RR more than 0.3 mV/ms were 98.3%, and those of less than 0.3 mV/ms were 1.7%. In contrast, MUAPs from BIC muscle with an RR of more than 0.3 mV/ms were 93%, and those of less than 0.3 mV/ms were 7%. We conclude it is better to use RR than RT when accepting MUAPs in clinical EMG, because even when sharp sounds are heard, MUAPs do not always have an RT of less than 500 microseconds. The use of RT and the sharpness of MUAPS therefore need to be reconsidered, or RR should be used in clinical EMG by automatic program.

Action Potentials↗
PubMed1997

Transcranial magnetic stimulation-induced changes in EEG and responses recorded from the scalp of healthy humans.

We determined the changes and responses in the electroencephalogram (EEG) induced by transcranial magnetic stimulation (TMS) of the scalp of five healthy men. The center of a circular coil was positioned at the vertex, and 80 stimulations were administered clockwise with the maximum output of electric current. To reduce stimulus artifacts, we created a circuit that blocked the input for 150 ms after stimulation. EEGs were recorded from F3,4, C3,4, P3,4, and T3,4. The following results were obtained: (1) slowing of the EEG was observed immediately (150 m) after each stimulation. The incidence of changes ranged from 25-80%; their duration ranged from 200-600 ms. (2). Electroencephalographic responses in the averaged form appeared as gentle positive waves. In some subjects and leads, 1 to 3 negative peaks were fused. The methods used in the present study may be useful in evaluating the sensitivity to TMS of patients with stroke and other types of brain injury.

Adult↗
PubMed1995

Motor unit firing behavior in slow and fast contractions of the first dorsal interosseous muscle of healthy men.

The motor unit recruitment threshold and firing rate were evaluated during slow and fast contraction of the first dorsal interosseous (FDI) muscle by healthy young men. Using a special quadrifilar electrode myoelectric activity was recorded during voluntary isometric contraction. Motor unit action potentials (MUAPs) were decomposed into individual MUAP trains by the electromyography (EMG) signal decomposition technique. Recruitment thresholds of the motor units decreased with the increase in the speed of contraction, and there was no recruitment reversal despite the increase. In terms of rate coding, the firing rates of the motor units increased as the speed of contraction increased; however, a high threshold motor unit always had a lower firing rate than a low threshold motor unit regardless of the contraction speed. At all contraction speeds, recruitment and rate coding may act through the same mechanism. If excitation of the motoneuron pool occurs rather than excitation of an individual motoneuron, a low threshold motor unit is easier to recruit and fire repetitively than a high threshold one. The motor unit firing behavior during fast contraction basically may be the same as during slow contraction.

Action Potentials↗
PubMed1994

Macro-EMG and motor unit recruitment threshold: differences between the young and the aged.

The relationship between macro-EMG (electromyography) and motor unit recruitment threshold was studied in the first dorsal interosseous (FDI) muscle of normal young and aged subjects. During voluntary isometric contraction, motor unit action potentials (MUAP) were collected by a special quadrifilar electrode and decomposed to each MUAP train (MUAPT) using an EMG signal decomposition technique. Macro-EMG was obtained from the electrode shaft, then triggered and averaged for each MUAPT. A positive linear correlation was observed in both the young and aged subjects. However, the correlation coefficients were significantly lower in the aged individuals than in the young individuals.

Action Potentials↗
PubMed1994

Motor unit firing behavior in man.

Studies on motor unit firing behavior in man by the decomposition technique are described. The decomposition technique identifies motor unit firing with 100% accuracy at force levels of greater than 80% maximal voluntary contraction (MVC). In all muscles examined, the higher the recruitment threshold of the motor unit, the lower the rate at which it fired at the target level. Smaller muscles, such as those in the hand, recruit their motor units at 0-50% MVC and rely exclusively on firing rate increases to augment force output at 50-100% MVC. Larger muscles, such as those in the leg or arm, recruit motor units at least to 90% MCV, and possibly higher. Their firing rates have a relatively smaller dynamic swing. Thus, smaller muscles rely primarily on firing rate and larger muscles rely primarily on recruitment to modulate their force. High cross-correlation functions in firing rate behavior within a muscle were observed between individual motor unit firing rates at constant force isometric contraction. Thus the nervous system does not control the firing rate of motor units individually. Instead, it acts on the pool of homonymous motoneurons in a uniform fashion. Electrical stimulation of cutaneous receptors tends to increase the recruitment thresholds of low-threshold motor units and to decrease their firing rates, while high-threshold motor units generally exhibit a decrease in recruitment threshold and an increase in firing rate.

Action Potentials↗
PubMed1991

Effects of percutaneous stimulation on motor unit firing behavior in man.

Motor unit firing behavior in human first dorsal interosseous (FDI) muscle was studied during controlled constant force isometric contractions. The threshold at which motor units were recruited and the mean firing rate at 50% of maximal voluntary contraction (MVC) were evaluated following stimulation of the skin area over the second digit. Stimulation of cutaneous receptors tended to increase the recruitment threshold of most of the motor units recruited under 20% MVC, while high-threshold motor units (those recruited over 30% MVC) generally exhibited a decrease in recruitment threshold. Less dramatic changes in motor unit firing rates were observed, but those motor units recruited over 30% MVC exhibited some increase in firing rate. The relationship between the change in recruitment threshold and change in motor unit firing rate is not rigid and seems to be susceptible to considerable synaptic noise.

Action Potentials↗
PubMedDate not supplied

Relation between macro-EMG and muscle Uber conduction velocity.

We investigated the relationship between macro-EMG and muscle Uber conduction velocity in the right biceps brachii in 5 normal subjects using a single-Uber macroelectrode and surface array electrodes. The macro-EMG signal and the surface electrode signals were triggered and averaged by the single-Uber action potential. The amplitude and area of the macro-EMG was correlated with the muscle Uber conduction velocity, suggesting that the macro-EMG can serve as a parameter of the size principle in both the clinical and research settings.

Adult↗