Biomedical subjects

Junichi Ushiba

Publications and source records attributed to Junichi Ushiba.

5 recordsLinked to original sources

PubMed2005

Inhibition from the plantar nerve to soleus muscle during the stance phase of walking.

The purpose of this study is to investigate the effect and the circuit from the branch of tibial (plantar) nerve to soleus muscle and its modulation during walking in humans. Stimulation of the plantar nerve produced short latency inhibition of soleus EMG activity and the H-reflex in humans. The threshold of afferent fibers was lower than that of motor fibers. This inhibition did not converge to disynaptic reciprocal Ia inhibition nor did inhibition from the cutaneous nerve of the big toe, but to Ib inhibition from the medial gastrocnemius nerve. The inhibitory pathway from the plantar nerve therefore is considered to include Ib inhibitory interneurones. Modulation of the inhibition was investigated during walking. Less EMG depression after plantar nerve stimulation occurred in the stance phase of walking than for tonic or dynamic plantar flexion at similar background EMG activity level. The inhibition of the soleus H-reflex after plantar nerve stimulation was also decreased during the stance phase. For investigating the influence of load on the inhibition from the plantar nerve, more EMG depression occurred in the stance phase with body unloading. Similar findings were observed in Ib inhibition from the medial gastrocnemius nerve, but not in disynaptic reciprocal Ia inhibition to soleus muscle. It is concluded that transmission of inhibition from the plantar nerve to soleus muscle is modulated during walking. It would minimize this inhibition during the stance phase of walking and might enhance soleus muscle activity via this reflex pathway for the support of weight.

Adult↗

PubMed2003

Reassessment of parameters for applying motor-unit triggered stimuli in peri-stimulus time histograms.

We reassessed the response properties of peri-stimulus time histograms (PSTHs) in cases when a test stimulus was triggered by a motor-unit discharge with a constant delay time. In this experiment, single motor unit action potentials were recorded from the right tibialis anterior (TA) muscle of five healthy persons. A test stimulus of the common peroneal nerve with low intensity to activate only Ia afferents of the TA was applied through a bipolar stimulating electrode placed distal to the neck of the fibula. We obtained several PSTHs with various delay times and stimulus intensities in the same recording session for maintaining the background property as the same among the test situations. As a result, we confirmed three characteristics of PSTHs from observed data: (1) given the same delay time (the same background firing properties), a weaker stimulus intensity evokes a lessened effect on PSTHs, naturally; (2) delay time alters the induction balance of direct and indirect effects on PSTHs even if the stimulus intensity is the same because the background firing properties are different; and (3) response probabilities do not correspond directly to stimulus intensities when background firing properties are different; it is possible for a relatively strong intensity stimulus to produce a weaker effect than a weak stimulus. We concluded that comparisons of effects taken at different phases in the control distribution (and also effects taken from different control distributions or different motor units) can be misleading. Therefore, such comparisons should only be made within data obtained from the same phase in the same control distribution of the same motor unit.

Adult↗

PubMed2003

Formula-based approach of statistical tests for peri-stimulus time histograms.

We introduce formula-based approaches for statistical tests regarding peri-stimulus time histograms (PSTHs) in cases when a conditioning stimulus was triggered by a motor-unit discharge with a constant delay time. The individual bin test and the cumulative sum test have recently been reported as methods for the quantitative analysis of PSTHs in the evaluation of human neural projections. These tests calculate confidence intervals using simulated point processes on the discharge of a motor unit, but require a significant amount of calculation time for the point process simulation. In order to overcome such a disadvantage in practical use, we provide a statistical formulization of the two above-mentioned tests using a combination theory. In general, the time required for calculating confidence intervals using these formula-based approaches was 2-13 times faster than when using the previous approaches. Unlike the previous ones, these formula-based approaches do not need to judge that a simulation process converges to the substationary state, and calculate an ideal distribution of statistical noise on the histogram, thereby providing high accuracy. We conclude that the formula-based approaches increase reliability and are sufficiently sophisticated for practical use.

Action Potentials↗

PubMed2002

Synchronization analysis using joint peri-stimulus time histograms for human motor units.

The concurrence of action potentials from two motor units (MUs) happens more frequently in human than what one would expect by chance. It can be visualized as the central peak of the Cross-Correlogram of spike trains from two MUs. It is widely believed that a common pre-synaptic input to motoneurons from the cortical tract generates the concurrence. A number of synchronization indices have been proposed in order to evaluate the quantity of the common input, however, these indices are dependent on the firing rates of the MUs. To resolve this issue, we introduce a new synchronization index beta using a joint peri-stimulus time histograms (JPSTH). In this paper, we discuss the dependence of synchronization indices on firing rates using a spike model, and the application of JPSTH and the index beta to experimental data for the quantitative analysis of MU synchronization. We confirm that the novel index beta represents the synchronization state independently from firing rates, and that it also accurately traces event-related temporal modulation of synchronization. In conclusion, we consider the index beta to be a valuable index for the analysis of MU synchronization.

Action Potentials↗

PubMed2002

A cumulative sum test for a peri-stimulus time histogram using the Monte Carlo method.

We have established a cumulative sum (CUSUM) test for a peri-stimulus time histogram (PSTH) for the case where a conditioning stimulus is delivered at a fixed interval after previous discharge of a motor unit. (We refer to this kind of PSTH as an 'arranged PSTH'). Expectations of the firing probability after the conditioning stimulus vary among the bins in this arranged PSTH, while the expectations among the bins are all the same in the original PSTH; thus, we could not apply conventional tests for statistical analysis. We, therefore, propose a novel CUSUM test that uses the Monte Carlo method. With this method, the range of the statistical scattering noise on a CUSUM is computationally found by simulating the statistical process in order to calculate the confidence interval. We verified this CUSUM test using both simulated and actual experiments. This paper presents the procedure for performing this new method, along with an example of its application.

Membrane Potentials↗