Recently, expectation toward MEG as a noninvasive tool to observe higher brain functions rises. However neuromagnetic fields associated with higher functions are very week, and it is necessary to average the fields over more than several tens trials. During MEG recordings, subjects are usually requested to reply the answer to the task with pressing a button or orally according to judgement, where the MEG responses related to the task and to the motor activities should not overlap each other. In this study, MEG responses during visual word discrimination in a button-press paradigm, that is, the button was pressed in every trial, were measured to reveal the time relationship of neural activity between the word processing and the motor reaction. In the responses averaged by two different ways of time locking at the stimulus onset (stimulus-lock average) and at the button-press time (button-press-lock average), the waveform was very different, where distinct MEG peaks were observed in each response. From the stimulus-lock average, where response peaks were observed between 150 and 850ms in both hemispheres, ECD sources at 150-600ms were localized in the areas which may be associated with word processing. From the button-press-lock average, response peaks were observed between -200 and +50ms, and ECD sources were localized in the areas associated with finger motion. Therefore, these activities were different in the waveform and in the source location, suggesting that the button-press paradigm can be used to observe higher brain functions.

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Mechanical impedance of soft living tissue is important for the understanding of the mechanical characteristics of the tissue and for the design of biological-sound transducers. Many studies have been done to date and Oestreicher's theoretical analysis has been commonly used. His modeling, the oscillating sphere in infinite viscoelastic medium, brings a computationally convenient analytic solution; however, the validity of such drastic simplification is not theoretically discussed yet. In the field of elasticity engineering, mechanical impedance of an oscillating disc on a semi-infinite elastic solid has been solved in several ways. We apply Robertson's solution to viscoelastic medium by introducing complexnumbered Lamé's constants and we calculate mechanical impedance of soft living tissue based on the model of an oscillating disc on a semi-infinite viscoelastic medium. This modeling has more accurate boundary conditions than the conventional one. Because of this realistic modeling, however, its solution needs complicated numerical calculation and is not intuitive. Therefore we derive a simple approximate formula of impedance by combining the first two terms in the expansion of the exact solution with an additional-mass term in the corresponding acoustic radiation impedance. The derived three-term approximate formula is accurate up to several or 10kHz, i. e. in the frequency range where the impedance is determined by shear elasticity and shear viscosity of the medium. The formula can be applied to many problems. We estimate the coefficient of shear elasticity and the coefficient of shear viscosity of soft living tissue and show that the estimate based on the conventional model underestimates these constants.

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To obtain useful data for establishing safety criteria for use of a pulsed Nd:YAG laser, intraocular pressure waves induced by radiating fundamental mode-Nd:YAG laser pulses (λ=1, 064nm), the second (λ=532nm), and the third (λ=355nm) harmonics were investigated. The radiation was delivered to extracted bovine eyeballs at various energies. Intraocular pressure waves generated were detected using a piezoelectric-type pressure sensor in the vitreum. Although the peak pressure increased with increased radiation energy at all wavelengths, there was a specific point on the radiation energy-peak pressure curve in the cases of the fundamental mode and the second harmonic above which the increasing rate of the peak pressure slowed. Retinal disruption was observed at radiation energies above this point. This result suggests that the specific point relates to the retinal optical breakdown threshold. In cyclic exposure tests under varied radiation energy above this point, the peak pressure at the second exposure decreased to about one-tenth of that at first exposure, and there was no significant change in peak pressure after the third exposure. This suggests that serious disruption of the retina and choroid in the focal region can be caused by only one exposure. In the case of exposure to the third harmonic, no change in peak pressure under the cyclic exposure tests and no retinal disruption were observed.

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The effect of an actively controlled stretcher (ACS) for an ambulance on the reduction of blood pressure variation during brake is discussed. Applying of the brake generates foot-to-head acceleration to the transported patient and causes the rise of the blood pressure at the head. There is a possibility that the blood pressure variation aggravates the patient's condition and causes the increase of the number of DOA (Dead On Arrival). The ACS has a tilting mechanism to absorb the foot-to-head acceleration by applying the gravitational acceleration. Desired angle of the ACS is calculated from the ambulance acceleration and the tilting angle is controlled actively. Emergency brake tests are performed to measure the continuous blood pressure in the finger of ten healthy male volunteers when the ACS is fixed or actively controlled. The position of the finger where the blood pressure is measured is set at eye level or the side of the waist to show the characteristics of the blood pressure variation in the body. Two kinds of indexes are proposed to indicate the effect of the ACS: one is root mean square value of the blood pressure variation which shows long-term change of the blood pressure and the other is maximal and minimal value of the blood pressure variation which express instantaneous change of the blood pressure. The experimental results show that the ACS stabilizes the long-term variation of the blood pressure and reduces the instantaneous change of the blood pressure at the eye level by 40 per cent compared with the conventional stretcher.

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The power spectral density function of the biological signal is a useful index in biological information processing. The biological signal is non-stationary and varies along with the influence of physiological factors and the external environment. The wavelet transforms is suitable for spectral analysis of non-stationary signals. We examined here, the usefulness of the application method of wavelet transforms to estimate an accurate power spectral density function from the biological signal. Moreover, we described the size of time-window, the frequency intervals of the power spectral density function and the calculating method of the power or amplitude. The proposed method was evaluated using the simulation data and the beat-to-beat interval time series. The results, showed that this method was useful to accurately estimate the power spectral density function of the signal.

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To study the brain temperature rise before powerful exercise, we measured the temperature in the external auditory meatus (EAM) and the facial temperature. Subjects had an exercise in which they pulled the back muscle dynamometer as quickly and powerfully as possible and maintained it at the most powerful position for 10 s. The subjects were instructed to keep their eyes closed during the exercise. Temperature in EAM was measured by IR-camera with an IR-optical fiber. Facial temperature was measured by an IR-camera. Thermal images were recorded every 0.1 s with a real time recorder. EEG at F₇ and F₈ on the forehead and EMG on the right medial gastrocnemius muscle were recorded simultaneously on a magnetic tape of a data recorder. EAM temperature was calibrated to body temperature using a regression curve calculated by the difference between ambient temperature and an object temperature. Facial temperature was calculated per m². The recorded EEG signal was analyzed by a FFT program in our laboratory. The power spectrum density (PSD) in the EEG frequency was calculated every 0.1 s. While a subject determined a position of feet and stance for an exercise, EAM temperature and facial temperature of the forehead increased, and surface EMG showed small amplitude activity. Facial temperature of the lower region did not change. When the temperature in EAM and forehead raised just before exercise, PSD in EEG of β-wave increased and PSD of α-wave decreased. The results of EMG and EEG activities show how exercises were prepared. Furthermore, it has been resulted that the temperature change in EAM and forehead were raised at the same time during exercise preparation. It is suggested that these alterations of temperature were related to physiological information during exercise preparation like EEG and EMG.

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The purpose of this study is to develop a method with which the mechanical properties of the femoral neck in vivo can be quantitatively evaluated. Modal analysis using the FEM (Finite Element Method) was made to investigate the relationship between Young's modulus of the femoral neck and the resonant frequencies of the femur. The configuration of the finite element model was generated from the CT images of an excised femur obtained from a male cadaver. Reduction of the flexural rigidity of the femoral neck was simulated by sequentially decreasing Young's modulus of the neck in the finite element model. The resonant frequency of torsion decreased more acutely than that of lateral bending as Young's modulus of the femoral neck was decreased. On the other hand, sequential transections were experimentally made in the neck of the femur in order to confirm the validity of the results in the model. The resonant frequency of torsion showed an acuter decrease as the depth of transection increased (i.e. with decrease of the flexural rigidity of the femoral neck) than the lateral resonant frequency. The results of the experimental neck transection were consistent with those of FEM analysis. From the observation of animated vibration modes using the FEM, it was found that torsional vibration was accompanied by bending vibration and that an antinode of the vibration was at the femoral neck. A decrease in the flexural rigidity of the femoral neck was thought to have a stronger effect on the resonant frequency of torsion than on that of bending because there was an antinode of the torsion accompanied by bending at the femoral neck. These results suggested that the resonant frequency of torsion could be one of the parameters reflecting the mechanical property of the femoral neck.

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We developed a motor-driven joint exerciser for the hip and knee incorporating three-dimensional load sensors in the thigh and calf supports of the machine. The machine can memorize and replay exactly the same exercise as therapists teach with three degrees of freedom of motion in the median plane. The previous investigation focuses on the virtual mechanical impedance control which enables soft movement like the exercise for the spastic joints by the human therapists. In this study we proposed the new controls adding the integral term to the equation for the impedance control so that the machine could stretch the stiff joint overcoming resistive joint force. Numerical calculation could show the new controls worked well both for the stiff and spastic joints. We installed the new controls in the machine, and demonstrated stretching effects of the controls on the stiff hamstrings muscles.

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