Influence of location of acceleration sensor on physiological tremor of upper limb.

The physiological tremor of the upper limb in three positions of pronation, neutrality, and supination due to the movement of forearm was measured on four locations at the tip of the finger, the root of the finger in the hand, the wrist, and the elbow with use of an accelerated sensor. The evaluation of the total power, which was the summation of the power spectrum in the frequency range from 1 to 50 Hz, showed no significant difference in any of the positions. The maintenance of the upper limb at the horizontal level showed the coordination of the central nervous system due to the body parts of the upper arm, forearm, hand, and finger connected by the joint. The coherence spectra showed clear activation of the joint of the wrist in the main peak frequency of around 2.5 and 12.5 Hz in their respective positions. The value of the correlation coefficient in the location between the hand and finger was the largest at over 0.8, and those of the locations which connected the joint of the wrist between the forearm and hand and between the forearm and finger were significantly large with a value from 0.6 to 0.8. The mean time (i.e., arrival time) of the transmission from the proximal side (i.e., upper arm and forearm) to the distal side (i.e., hand and finger) in the upper limb was evaluated quantitatively to be 20 ms for pronation and supination, but the value was small for neutrality.

Cortical potentials associated with voluntary, reflex, and spontaneous blinks as bilateral simultaneous eyelid movement.

Movement-related cortical potentials (MRCPs) associated with the contraction of m. orbicularis oculi related to three types of blinks (voluntary, reflex, and spontaneous) were measured for 12 normal subjects. The purpose of the present study was to estimate the role of the cerebral cortex in close association with the blinks caused by bilateral simultaneous eyelid movements. MRCPs were recorded by surface electrodes placed over the frontal to the parietal regions. The mean amplitude and the duration of the MRCPs for the three types of blinks were evaluated by an averaging technique for each subject. MRCPs for the voluntary blinks were evoked in all subjects. For the reflex and the spontaneous blinks, however, a clear negative rising deflection from the baseline was not obtained. The maximum amplitude of the MRCPs for the voluntary blinks was localized at the vertex region, though there was no significant difference between the durations of the MRCPs for the vertex region and for the other regions. Moreover, the positive potential following the voluntary and the spontaneous blinks was recognized in the parietal region. These results suggest that only the voluntary blinks are caused by the neural activation of the supplementary motor area (SMA), and in addition, the neural activation related to visual recognition is considered to be elicited by the voluntary and the spontaneous blinks.

Influence of hyperbaric environment on physiological tremor.

The effect of pressured environment from 1 to 24 ATA (Atmosphere Absolute) on total power spectrum (TP) of physiological tremor, whose value was the sum of power spectra for frequency range in 0.5-50 Hz, was investigated. The main effects obtained were as follows. (1) In the case of 3 ATA, TP during the pressure holding period denoted a similar value as the value in 1 ATA. In the latter half of the period, the TP increased. When the pressured environment is 4 ATA, in which the partial pressure of the nitrogen gas was 3.6 ATA, the TP decreased during the pressure holding period compared with the value in 1 ATA. Nitrogen narcosis was recognized at the partial pressure of 3.6 ATA, thus the effect denoted a decrease of TP. (2) In the cases of 16 and 19 ATA using heliox gas, during the pressure holding period, TP decreased compared with the value in 1 ATA, but in the case of 24 ATA the value increased. The partial pressure of helium gas of 23.6 ATA indicated a high pressure nervous syndrome, therefore, the influence of high pressure on TP was recognized as one of the causes of the increase of TP. (3) The influence of inhibitors of the autonomic nervous system on TP during the pressure holding period of 3 ATA was recognized. After intake of the inhibitor for the parasympathetic nerve (atropine) during the pressure period, TP increased, while for the intake of the inhibitor for the sympathetic nerve (propanol), TP decreased.

Paradoxical phenomenon of physiological tremor in prolonged tapping load.

Cumulative fatigue caused by a tapping load is investigated by power spectrum analysis of both physiological tremor of the finger and surface electromyogram (EMG) of the forearm muscle controlling the finger. A load for two hours at a rate of 200 taps/minute is performed on ten male subjects. The physiological tremor and the EMG are measured before and during the load. The measurement is performed under the isometric contraction at 10% maximum voluntary contraction in the m. flexor digitorum superficialis. The total power and the slow wave ratio of the power spectrum are evaluated. During the load, both spectra of the physiological tremor and the EMG show the maximum total power at 30 minutes after the load. The total powers of both spectra, however, decrease in the period after 60 minutes. Namely, the results of the physiological tremor and the EMG for prolonged load show the "paradox of fatigue." In order to elucidate the cause of the paradox of fatigue, the slow wave ratio of the EMG spectrum is studied. The ratio increases during the load. The muscle loaded indicates the state close to exhaustion, and the change of the function of the muscle contraction affects the amplitude of the physiological tremor. Therefore, the criterion judging muscular fatigue is denoted due to the change of the amplitude of the physiological tremor.

Physiological tremor of the upper limb segments.

The acceleration signal produced by physiological tremor from four different upper limb segments (the finger, hand, forearm and upper limb) was measured by an acceleration sensor during holding posture and was analyzed by power spectrum analysis. Two prominent peaks appeared in the power spectrum, suggesting that the tremor in the four different limb segments was composed of two frequency components. The frequency of one peak at 8-12 Hz did not change between the different limb segments, while the frequency of the other peak decreased with the increase in the mass of the limb segment. A model with two reflex pathways was developed for the tremor in the four limb segments. The model includes two reflex pathways, a spinal pathway and a supraspinal pathway. The theoretical values of the frequency and the amplitude of the tremor predicted by the model were in good agreement with the experimental results. Analysis of the model revealed that one of the two frequency components of the tremor was of spinal origin and was dependent upon the mass of the limb segment, and the second was of supraspinal origin, corresponding to the frequency at 8-12 Hz. In the normal subject, it is possible that the tremor could be used to evaluate the change in neuromuscular function produced by prolonged work involving just part of a limb segments (e.g., typing). It may also be used to evaluate the neuromuscular function of patients suffering from neurological diseases such as muscular dystrophy and Parkinson's disease.