The conditioning of cortical excitability by transcranial magnetic stimulation (TMS) has become a valuable technique to promote recovery of motor function after stroke. As TMS is not used in all ...patients, we investigated the hypothesis that peripheral stimulation may have an adjustment effect on motor cortical excitability. Our experimental paradigm was divided into three phases. In the first phase, TMS was delivered to the left or right primary motor cortex to induce a motor evoked potential (MEP) from the contralateral first dorsal interosseous muscle. The measured MEPs in this phase were used to evaluate the effect of peripheral stimulation. In the second phase, 1 Hz magnetic stimulation was applied over the contralateral or ipsilateral forearm for motor cortex as peripheral stimulation. In the third phase, the MEP was evoked by TMS and recorded using the same setting as the first phase. We found that a decrease in MEP amplitude was observed in the left motor cortex following peripheral stimulation over the right forearm. By contrast, the MEP amplitude was not altered in the right motor cortex by peripheral stimulation over the left forearm. An increase in MEP amplitude was observed in the ipsilateral motor cortex induced by peripheral stimulation over the left or right forearm. We also found that by changing the MEP amplitude, the motor cortex excitability varied according to magnetic stimulation of the forearm. These data suggest that peripheral stimulation may have an adjustment effect on motor cortical excitability, via changes in the stimulus site.
A new method is proposed for describing the shape of the induced artifact in the electroencephalography (EEG) applied transcranial magnetic stimulation (TMS) using two equivalent circuit models, the ...TMS equipment model and the equivalent circuit model of bioelectric measurement system. The TMS equipment circuit is switched into three modes, and one of them is the oscillation mode by a capacitance in the equipment and a TMS coil. The electromagnetic induction from the TMS coil to the brain in this mode corresponds to the TMS. The bioelectric measurement system forms a closed circuit by a bioelectric equivalent circuit and an EEG measurement system, and the TMS induces the electromotive force into the closed circuit. The artifact induced by the TMS is measured as the TMS artifact, which is appended to the measured EEG. Under some simplified approximations, the TMS artifact is expressed by two modes, the TMS oscillation mode and the discharge mode, and the solutions of the TMS artifact are solved from circuit equations for each mode. The simulation output calculated from these solutions successfully describes the TMS artifact in the measured EEG data by considering the frequency property of the bioelectric circuit parameters.
The entire process of oxygen transport in microcirculation by developing a3 D porous media model is calculated numerically with coupled solid deformation-fluid seepage-convection and diffusion. The ...principal novelty of the model is that it takes into account volumetric deformation of both capillary and tissues resulting from capillary fluctuation. How solid deformation, fluid seepage, and convection-diffusion combine to affect oxygen transport is examined quantitatively：（1） Solid deformation is more significant in the middle of capillary, where the maximum value of volumetric deformation reaches about 0.5%.（2） Solid deformation has positive influence on the tissue fluid so that it flows more uniformly and causes oxygen to be transported more uniformly, and eventually impacts oxygen concentration by 0.1%–0.5%.（3） Convection-diffusion coupled deformation and seepage has a maximum（16%） and average（3%） increase in oxygen concentration,compared with pure molecular diffusion. Its more significant role is to allow oxygen to be transported more evenly.
In this study, we investigate the relationships between the eddy current density and the coil configuration of transcranial magnetic stimulation (TMS). The aim of this study is to determine the coil ...parameters such as the radius of the coil and the bending angle of the coil to stimulate specified area such as the dorsolateral prefrontal cortex (DLPFC). We used a realistic 3-D human head model with inhomogeneous conductivity to obtain accurate eddy current distributions. In the TMS model, eddy current distributions were obtained for figure-eight coils with radius of 30, 40 and 50 mm, and a bending angle of the coil changed from 0 to 30 degrees. Computer simulations show that the maximum value of the eddy current increases linearly with the increase of the radius and the bending-angle of the coil. The maximum eddy current density was 87.6 A/m 2 under the case where the bending-angle was 30 degrees and the radius was 50 mm. The stimulated area increased with the increase of the radius and bending-angle of the coil. It is possible to determine coil parameters to stimulate target area appropriately.
A high spatial resolution superconducting quantum interference device (SQUID) system was developed. This SQUID system enabled measurement and discrimination of the magnetic field pattern under ...800-mum resolution. Magnetic fields produced by the compound nerve action current of the frog sciatic nerve were measured. The compound action potential and compound action magnetic fields when the stimulus current changes from 0.2 to 1 mA were measured. It was possible to observe that several components of the compound action magnetic fields have different conduction velocities in different kinds of fibers of the nerve bundle within 4 ms after stimulation. When the stimulus intensity increased, the waveform of the compound action potential changed and the duration of the late component of the compound action potential became longer. We found that this change was caused by the excitation of the nerve which has slow conduction velocity. We also succeeded in measurement of the auditory evoked magnetic fields of mice with high spatial resolution. The polarity change of peak magnetic fields appear in the 10-mm area. It is difficult to detect these signals using a SQUID magnetometer with a large size pickup coil or measurements of action potential.
The combination of transcranial magnetic stimulation (TMS) and an electroencephalogram (EEG) is an effective tool for investigating the functional connectivity in the brain. This paper investigated ...cortical reactivity and connectivity by the combination of TMS and EEG. The spontaneous activity of the brain was measured before and after magnetic stimulation. The effect of TMS on alpha activity was investigated. The alpha wave was suppressed for a few seconds after stimulation of the occipital area. No differences in the suppression of the alpha waves were found with and without auditory masking. Furthermore, the coil click of TMS had no effect on the alpha wave. The alpha wave was significantly suppressed by the occipital stimulation, whereas slight suppression was observed in other areas of stimulation. The alpha wave was increasingly suppressed as the stimulation magnitude became more intense. In order to investigate the evoked response by TMS, evoked potentials generated by TMS were measured. It was observed that more evoked responses spread to the center of the brain when the cerebellum was stimulated than at other areas of stimulation. These results indicated that TMS blocked the neural connections within alpha wave generation, and the electrical currents produced by TMS affected the neural activities.
Transcranial magnetic stimulation (TMS) is the non-invasive stimulus method to the brain by inducing the eddy current within the brain from the TMS coil placed outside the scalp. The induced eddy ...current stimulates the nerve circuit causes to suppress the brain activity partially in time and space, and it is applied to detect the brain functions etc. When TMS is applied to the brain while measuring the electroencephalography (EEG), the induced artifact caused by TMS covers on the EEG, it is called the TMS artifact. The amplitude of the TMS artifact is generally too large to omit diagnosing the EEG. Therefore some methods have been proposed to negate the TMS artifact from the EEG including the TMS artifact using the EEG only. We proposed a new method for describing the shape of the induced artifact in the EEG applied TMS using two equivalent circuit models, the TMS equipment model and the equivalent circuit model of bioelectric measurement system, under some simplified approximations.
This paper shows that some attempts are applied to the proposed method to improve the performance of fitting and eliminating the TMS artifact. One is to derive the strict solution of the TMS artifact by omitting some simplified approximations. Other is the countermeasure against errors calculating inverse matrix while estimating parameters of fitting shape of the TMS artifact. One attempt is found that the strict solution improves the shape fitting but not so far from the approximated solution. Other attempt improves stability of the simulation. These attempts are found that some time parameters which determine the time-transition such as “Tc” should separately treat against other time constant parameters which are derived from circuit parameters. Moreover, considering the residual component this is not described on the circuit model.
