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Biomedical subjects

Nobuki Murayama

Publications and source records attributed to Nobuki Murayama.

5 recordsLinked to original sources
PubMed2006

Effects of visual stimulation on cortico-spinal coherence during isometric hand contraction in humans.

The effects of visual stimuli on cortico-spinal synchronization were investigated by measuring the coherence between electroencephalogram (EEG) and electromyogram (EMG) during isometric contraction of the first dorsal interosseous muscle of the right hand. Because a spinal motoneuron and the corresponding muscle fibers form a motor unit with one-to-one correspondence of their action potentials, the EMG indirectly measures the activity of the corresponding spinal neuronal group. The tasks were isometric contraction (Control condition); and isometric contraction with concurrent ignoring of visual stimuli (VS condition). By comparing the Control and VS conditions, the following results were obtained. The coherence increased significantly in magnitude, but was unchanged in frequency range (beta band) and scalp location; the EEG and EMG spectral power in the beta band were unchanged in amplitude; and the alpha and gamma bands of EEG spectral power were significantly increased and decreased, respectively. These findings suggest that the cortico-muscular coherence reflects the cognitive effort needed to maintain isometric muscle contraction. When visual stimuli need to be ignored, the cognitive effort and cortico-spinal coherence are enhanced.

Adult↗
PubMed2005

Influence of aging on cardiac function examined by echocardiography.

We assessed the influence of aging on cardiac function by means of parameters measured by echocardiography. The study group consisted of 494 normal subjects aged 13 to 87 years. We measured the ratio of early filling (E) and atrial contraction (A) transmitral flow velocities (E/A) of left and right ventricular inflow (LV E/A and RV E/A) for assessment of diastolic function. We also measured left ventricular ejection fraction (LVEF), and the ratio of pre-ejection period (PEP) and ejection time (ET) of the left ventricle (PEP/ET) for assessment of systolic function. Both LV E/A and RV E/A decreased significantly with aging while LVEF and PEP/ET remained normal range. The decline rate as aging was greater in LV E/A than in RV E/A. These results showed that both left and right ventricular diastolic function deteriorated with aging while left ventricular systolic function was not noticeably affected by aging. We suggest that indexes of diastolic function are more sensitive than those of systolic function when the natural course is studied in a large population.

Adolescent↗
PubMed2004

Subthreshold low-frequency repetitive transcranial magnetic stimulation over the premotor cortex modulates writer's cramp.

Writer's cramp, or focal hand dystonia, is characterized by involuntary coactivation of antagonist or unnecessary muscles while writing or performing other tasks. Although the mechanism underlying this muscle overactivation is unknown, recent studies of changes in cerebral blood flow during writing have demonstrated a reduction in the activation of the primary motor cortex (MC) and hyperactivity of parts of the frontal non-primary motor areas. Therefore, any measures that decrease the activities of non-primary motor areas such as the premotor cortex (PMC) and the supplementary motor area (SMA) might improve dystonic symptoms. To explore this possibility, we studied nine patients with writer's cramp and seven age-matched control subjects, using subthreshold low-frequency (0.2 Hz) repetitive transcranial magnetic stimulation (rTMS), which exerts an inhibitory action on the cortex. Previous studies have demonstrated shortened cortical silent periods in dystonia, suggesting deficient cortical inhibition in the MC. We compared the silent periods and computer-assisted ratings of handwriting before and after rTMS applied to the MC, SMA or PMC. We also used the sham coil for control runs. Stimulation of the PMC but not the MC significantly improved the rating of handwriting (mean tracking error from the target, P = 0.004; pen pressure, P = 0.01) and prolonged the silent period (P = 0.02) in the patient group. rTMS over the other sites or using a sham coil in the patient group or trials in the control group revealed no physiological or clinical changes. This increased susceptibility of the PMC in dystonia suggests that the lack of inhibition in the MC is secondary to the hyperactivity of PMC neurons. Inhibition of the PMC using rTMS could provide a therapeutic measure of writer's cramp.

Adult↗
PubMed2004

[Communication device utilizing event-related potentials].

We had developed a communication system using a theory of P300 through a computer. 17 healthy subjects participated in all 3 experiments, while 4 ALS and 1 OPCA patients took part in the first 2 experiments only. In the 1st experiment, 4 short sentences of 'yes very much', 'yes' 'no' and 'can't answer' were shown on the display. The subjects were asked to select one of them as target. During the experiment 1, color of background was randomly changed for each sentence as the stimulation for the period of 300 msec and the interstimulus interval was 1,500 msec. In the 2nd experiment, 46 letters of Japanese character and several symbols were shown on the display (5 columns x 10 rows). In the 3rd experiment, we used 16 pictures together with X (4 columns x 5 rows). During recordings, the color of background was randomly changed for each row and then for each letter/picture of column containing target in experiment 2 as well as in experiment 3. The subjects were asked to start counting and when the target was stimulated, they were instructed to stop the counting process and repeat counting again until they encountered the stimulation of target again. This was repeated for the entire recordings. Computer defined a target by a biggest positive voltage between 300 and 600 msec and/or by the most powerful spectrum in 2-5 Hz after Fast Fourier transform in an averaged P300 (averaging number = 5-7). We then calculated the percentage of correct target by comparing the result and actual target. Results indicate that this communication aids can be used conveniently in patients with severe motor disabilities.

Adult↗