Hirofumi Sekiguchi

Jobu University, Japan

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Publications (29)36.88 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Corticospinal excitability in the lower leg muscles is enhanced during standing as compared to other postures. In the present study, we investigated how the excitability of intracortical circuits that control the tibialis anterior muscle (TA) is modulated during standing. Short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed by the paired-pulse transcranial magnetic stimulation technique during standing (STD) and sitting (SIT) with a comparable background activity level in both the soleus and the TA muscle. The results demonstrated that SICI was less effective during STD than during SIT, whereas ICF was more effective during STD than during SIT. These findings suggest that the excitabilities of these cortical neural circuits are modulated depending on posture. A decrease in SICI and an increase in ICF may reflect subliminal enhancement of the cortical excitability in the TA muscle during standing as compared with that during sitting.
    Brain research. 06/2014;
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    ABSTRACT: In human movements muscles lengthen and then shorten, or occasionally shorten and then lengthen, but it is unclear whether the nature of neural activation of the initial phase influences the neural state of the subsequent phase. We examined whether contraction history modulates spinal excitability in the healthy human soleus muscle. Subjects performed six blocks of 10 repetitions of four muscle actions consisting of specific combinations of passive shortening (PAS), and passive lengthening (PAL), shortening contraction (SHO), and lengthening contraction (LEN); that is: (1) SHO+PAL; (2) PAS+LEN; (3) PAS+PAL; and (4) SHO+LEN. Compared with baseline, the H-reflex increased in the block of 300-400 s after SHO+PAL and decreased in the block of 0-100 s after PAS+LEN and SHO+LEN. Our results suggest that spinal excitability is potentiated during a muscle action preceded by muscle shortening, but it becomes depressed during a muscle action preceded by muscle lengthening.
    Muscle & Nerve 06/2011; 43(6):851-8. · 2.31 Impact Factor
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    ABSTRACT: Our purpose was to establish a technique to reduce residual artifacts after transcranial magnetic stimulation (TMS) from electroencephalographic (EEG) signals. We investigated the effects of coil direction and stimulus intensity on residual artifacts in an artificial circuit, and tested whether or not the size of the circuit area affects the residual artifact (the model study). Based on the results, the optimization by rearranging the electrode's lead wire was tested on the human scalp (the human study). The residual artifact after TMS was dependent on the direction of the figure-of-eight coil, and on the artificial circuit area size. In accordance with the model study, the scalp EEG shows that TMS-induced artifacts can be reduced dramatically before the amplifier input stages in TMS-EEG experiments by a step-wise procedure rearranging the lead wires relative to the fixed coil orientation. Our technique makes it possible to significantly reduce the residual artifacts from recordings of short-latency TMS-evoked potentials.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 09/2010; 122(5):984-90. · 3.12 Impact Factor
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    ABSTRACT: Stereotyped behaviors should be inhibited under some circumstances in order to encourage appropriate behavior. Psychiatrists have used the modified rock-paper-scissors (RPS) task to examine the inhibition of stereotyped behavior. When subjects are required to lose in response to a gesture, it is difficult for them to lose, and they have a tendency to win involuntarily. It is thought that the win response is the stereotyped response in the RPS task, and the difficulty in making positive attempts to lose is due to the requirement for inhibition of the stereotyped response. In this study, we investigated the brain regions related to inhibition of the stereotyped response using functional magnetic resonance imaging (fMRI). Subjects were assigned to one of two groups: the "win group" or the "lose group." The lose group showed higher activation of the left dorsolateral prefrontal cortex (DLFPC) when compared to the win group. We also delivered transcranial magnetic stimulation (TMS) while the subjects performed the modified RPS task to investigate whether the left DLPFC (middle frontal gyrus, Brodmann area, BA 9) was directly involved in the inhibition of the stereotyped response. When TMS was delivered before onset of the visual stimulus, the subjects displayed increased response errors. In particular, the subjects had a tendency to win erroneously in a lose condition even though they were required to lose. These results indicate involvement of the left DLPFC in inhibition of the stereotyped responses, which suggests that this region is associated with inhibition of the preparatory setting for stereotyped responses rather than inhibition of ongoing processing to produce a stereotyped response.
    Experimental Brain Research 06/2010; 203(3):593-600. · 2.22 Impact Factor
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    ABSTRACT: Musician's dystonia is a type of task specific dystonia for which the pathophysiology is not clear. In this study, we performed functional magnetic resonance imaging to investigate the motor-related brain activity associated with musician's dystonia. We compared brain activities measured from subjects with focal hand dystonia and normal (control) musicians during right-hand, left-hand, and both-hands tapping tasks. We found activations in the thalamus and the basal ganglia during the tapping tasks in the control group but not in the dystonia group. For both groups, we detected significant activations in the contralateral sensorimotor areas, including the premotor area and cerebellum, during each tapping task. Moreover, direct comparison between the dystonia and control groups showed that the dystonia group had greater activity in the ipsilateral premotor area during the right-hand tapping task and less activity in the left cerebellum during the both-hands tapping task. Thus, the dystonic musicians showed irregular activation patterns in the motor-association system. We suggest that irregular neural activity patterns in dystonic subjects reflect dystonic neural malfunction and consequent compensatory activity to maintain appropriate voluntary movements.
    Journal of Neurology 02/2010; 257(7):1092-8. · 3.58 Impact Factor
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    ABSTRACT: The purpose of this study was to investigate how the recruitment properties of the corticospinal pathway are modulated in the soleus (SOL) and tibialis anterior (TA) muscles depending on postures. A wide range of stimulus intensities were applied via transcranial magnetic stimulation over the primary motor cortex during standing (STD) and sitting (SIT) with a comparable background activity level in each muscle. The relationship between the stimulation intensities and the size of motor-evoked potentials was assessed by the Boltzmann sigmoid function, which is characterized by a plateau value, maximum slope, and threshold. The plateau value and maximum slope were significantly higher during STD than during SIT in the SOL muscle (STD vs. SIT, plateau value: 50.0 +/- 21.8 vs. 33.9 +/- 12.3 mV ms, maximal slope: 1.6 +/- 0.7 vs. 1.2 +/- 0.5 mV ms/% maximal stimulator output). Similar changes of the parameters were also observed in the TA muscle (STD vs. SIT, plateau value: 71.0 +/- 22.9 vs. 41.4 +/- 16.1 mV ms, maximal slope: 5.0 +/- 2.0 vs. 2.5 +/- 0.7 mV ms/% maximal stimulator output). The threshold did not differ significantly between the two conditions and both muscles. These results indicate that the central nervous system requires a different control for each postural condition; that is, the relative balance of the excitatory and inhibitory inputs to the corticospinal pathways as well as the number of neurons of subliminal fringe in the corticospinal pathway was increased during STD compared with those during SIT.
    Experimental Brain Research 09/2009; 197(3):207-13. · 2.22 Impact Factor
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    ABSTRACT: Stereotyped responses must be suppressed at certain times during daily life, which can be difficult for patients with lesions in the frontal cortices. Neuropsychologists have used the rock-paper-scissors (RPS) task to evaluate patients' ability to suppress a stereotyped response. In this study, we measured functional magnetic resonance imaging signals to investigate how frontal cortex activities change corresponding to subjects' performance as they tried to lose (successfully inhibiting the typical response to win) when presented with a gesture signifying rock, paper, or scissors. Performance rates ranged from 50% to 100%, and results indicated that activation in the bilateral anterior part of the prefrontal cortex increased parametrically corresponding to subjects' successful performance. This result implies that the anterior prefrontal cortex plays a key role in the successful completion of a modified RPS task and may play a role in the suppression of stereotyped responses.
    Neuroscience Letters 04/2009; 453(1):1-5. · 2.03 Impact Factor
  • Neuroscience Research - NEUROSCI RES. 01/2009; 65.
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    ABSTRACT: The purpose of this study was to investigate effects of long-term participation to swimming on adaptations of spinal reflex excitability. To this end, mechanically induced stretch reflex (SR) and electrically induced Hoffmann (H-) reflex of the soleus muscle were investigated between swimmers with experience of more than 10 years and non-trained individuals while sitting at rest. The amplitude and the gain (stretch velocity vs. amplitude of the reflex response) of the SR were significantly greater in the swimming group than in the non-trained control group. Similarly, the responses of the H-reflex were also significantly greater in the swimming group than in the non-trained control group. Results of this study demonstrated that the spinal reflex excitability in experienced swimmers was far more enhanced than in non-trained individuals.
    Arbeitsphysiologie 11/2008; 105(2):199-205. · 2.66 Impact Factor
  • Brain Stimulation - BRAIN STIMUL. 01/2008; 1(3):281-281.
  • Clinical Neurophysiology - CLIN NEUROPHYSIOL. 01/2008; 119(6).
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    ABSTRACT: The purpose of this study was to clarify the relationship between mechanical stress and tissue response of the contracted knee joint in rats and to propose a new design of contracture correction device for clinical use. Wistar rats were operated on to immobilize their knee joints with a procedure causing periarticular bleeding and were kept in flexed position for 40 days. At day 40, the immobilizing wire was removed, and after day 43, the contracted knee joint had been treated with tunable corrective devices secured by an external fixation method to the rear limb. These devices consisted of four types of motor-driving system which provided several different low-load and continuous stretch torques. Measuring the angle of maximum knee extension, its effectiveness was assessed comparing with a lower load and control group of natural recovery course. The device also had a cyclic joint movement within the acquired range of motion and an oval cam mechanism producing a small distraction force to the joint along its long axis. The results showed that an appropriate range of low-load continuous torque was more effective to correct joint contracture. On the basis of the animal experiment, a new computer-controlled, gas-driven contracture correction device was developed for clinical trial. It was concluded that mechanical application in a condition with low and continuous torque is a useful treatment for fixed joint contracture.
    Prosthetics and Orthotics International 07/2007; 31(2):121-32. · 0.62 Impact Factor
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    ABSTRACT: Lengthening and shortening contractions are the fundamental patterns of muscle activation underlying various movements. It is still unknown whether or not there is a muscle-specific difference in such a fundamental pattern of muscle activation. The purpose of this study was, therefore, to investigate whether or not the relationship between lengthening and shortening contractions in the modulation of corticospinal excitability in the first dorsal interosseus (FDI) muscle is the same as that of previously tested muscles because the hand muscles are anatomically and functionally different from the other muscles. To this end, we investigated the relationship between the input-output curves of the corticospinal pathway (i.e., the relationship between the stimulus intensities vs. the area of motor-evoked potentials) during lengthening and shortening contractions in 17 healthy subjects. The shape of this relationship was sigmoidal and characterized by a plateau value, maximum slope, and threshold. The plateau value was at the same level between lengthening and shortening contractions. However, the maximum slope (P < 0.01) and threshold (P < 0.01) were significantly higher during lengthening contractions than during shortening contractions. These findings were different from the results of other muscles tested in previous studies (i.e., the soleus muscle and the elbow flexors). That is to say, the plateau value and the maximum slope during lengthening contractions were significantly lower than those during shortening contractions in previous studies. This study provides tentative evidence that the relationship between lengthening and shortening contractions in the modulation of corticospinal excitability differs between muscles, indicating that the underlying neural control is not necessarily the same even though the fundamental patterns of muscle activation are carried out.
    Experimental Brain Research 04/2007; 178(3):374-84. · 2.22 Impact Factor
  • Neuroscience Research - NEUROSCI RES. 01/2007; 58.
  • Neuroscience Research - NEUROSCI RES. 01/2007; 58.
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    Annals of General Psychiatry 01/2006; · 1.57 Impact Factor
  • Yutaka Kohno, Yasoichi Nakajima, Hirofumi Sekiguchi
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    ABSTRACT: Transcranial magnetic stimulation (TMS)-evoked N100 component (TMS-N100) is a negative peak wave at about 100 ms after TMS to the motor cortex. To elucidate the contribution of somatosensory and auditory inputs to the generation of TMS-N100, and to determine the cognitive effect of this potential, we recorded TMS-N100 with the TMS-compatible whole-head 60-channel EEG system from 10 healthy subjects. The peak latencies and pattern of potential distributions were similar between TMS-N100 under the ignore condition and the potential evoked by SMT+AUD in 100 ms (SMT+AUD N1) under the ignore condition. The amplitude of TMS-N100 significantly increased under the cognitive condition, while the latency and the potential distribution of TMS-N100 were not changed. These cognitive effects were also observed on SMT+AUD N1 under the cognitive condition. Therefore, inputs of TMS-N100 are the magnetic stimulation to the cerebral cortex and somatosensory and auditory inputs accompanied with TMS. The amplitude of TMS-N100 is increased by performing the cognitive task, thus, the cognitive status should be considered when the amplitude of TMS-N100 is interpreted.
    International Congress Series 01/2005; 1278:284-287.
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    ABSTRACT: We investigated the modulation of the corticospinal excitability during lengthening (LEN) and shortening (SHO) contractions in the first dorsal interosseus (FDI) muscle. The maximum slope of input–output property (the relationship between stimulus intensities vs. motor evoked potentials) during LEN contractions was significantly higher than that during SHO contractions. However, after repetitive exercise training of LEN and SHO contractions for 2 weeks, the maximum slope during LEN contractions was significantly reduced. This result suggests that the FDI muscle is inexperienced in a significant number of LEN contractions in daily life.
    International Congress Series 01/2005; 1278:288-290.
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    ABSTRACT: To investigate the effects of loading and unloading of the lower limb joints on the soleus H-reflex in standing humans. H-reflexes were elicited in the soleus muscle in subjects standing on a force platform in a water tank under the following loading conditions of the ankle and knee joints: control condition; reduced loads of -10 and -20 N; imposed loads of 10 and 20 N. The joint loading was altered by changing the combinations of buoys and weights attached to the lower limb segments, while total body weight was kept constant. As the ankle- or knee-joint load was reduced, the H-reflex was significantly enhanced compared to that under the control condition. In contrast, the H-reflex was decreased as the ankle- or knee-joint load was increased. In both cases, similar levels of background activity were recorded. The present results suggest that joint afferents might mediate the suppression of the soleus H-reflex in standing humans. However, the identification of the receptors and/or the mechanisms cannot be addressed under the current experimental set up. The results of this study give some basic insights into reflex control in an upright posture.
    Clinical Neurophysiology 07/2004; 115(6):1296-304. · 3.14 Impact Factor
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    ABSTRACT: The purpose of the present study was to ascertain the contribution of peripheral sensory inputs to posture-related Hoffman reflex (H-reflex) modulation in the human soleus muscle. The soleus H-reflexes were elicited in the sitting (SI) and passive standing (ST) conditions in patients with clinically complete spinal cord injuries (SCI) and in neurologically normal subjects. The results clearly showed suppression of the H-reflex amplitude during the ST compared with the SI condition especially in the SCI group. Considering the lack of a descending neural command in the SCI patients, our findings suggest that peripheral sensory inputs primarily contribute to the reduction of the soleus H-reflex during the upright standing posture.
    Neuroscience Letters 08/2003; 345(1):41-4. · 2.03 Impact Factor