Publications (6)13.49 Total impact
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Article: TMS-induced artifacts on EEG can be reduced by rearrangement of the electrode's lead wire before recording.
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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 -
Article: The role of the dorsolateral prefrontal cortex in the inhibition of stereotyped responses.
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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. · 2.39 Impact Factor -
Article: An fMRI study of musicians with focal dystonia during tapping tasks.
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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. · 3.47 Impact Factor -
Article: Anterior prefrontal cortex activities during the inhibition of stereotyped responses in a neuropsychological rock-paper-scissors task.
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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. · 2.11 Impact Factor -
Article: Modulation of corticospinal excitability during lengthening and shortening contractions in the first dorsal interosseus muscle of humans.
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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. · 2.39 Impact Factor -
Article: Short latency TMS-evoked scalp-recorded potentials
Annals of General Psychiatry. 01/2006;
