Osamu Hiwaki

A method for estimation of stimulated brain sites based on columnar structure of cerebral cortex in transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is a noninvasive method to stimulate the cortex. In TMS with a figure-of-eight coil, the induced electric field elicited by the pulsed magnetic fields is gathered beneath the center of the figure-of-eight coil, so the point on the cortex beneath the center of the figure-of-eight coil has been regarded as a stimulating site conventionally. However, the stimulating point determined in this way is not supposed to be plausible because electric field induced in TMS is dispersed over the brain vectorially. The present study proposed the novel method for the accurate estimation of stimulating points of the cortex in TMS. In our proposed method, the cortical structure and property of neural excitation in magnetic nerve stimulation were taken into account. The basic unit of the cerebral cortex is the cylindrical column containing pyramidal neurons perpendicular to the cortical surface, and neural excitation in the magnetic nerve stimulation is determined by the spatial deriv...

Precise coil positioning system using multi-articular arm for location of stimulated brain area in transcranial magnetic stimulation

We developed a precise coil positioning system for determining stimulated sites in transcranial magnetic stimulation (TMS) by using a multi-articular mechanical arm. A figure-of-eight coil used in TMS can induce a focal electric field beneath the coils center in the cortex; therefore, the point on the cortex beneath the center of the figure-of-eight coil has been conventionally regarded as a stimulating site. However, a stimulating site determined in this manner is not believed to be plausible, because the electric field induced in TMS is dispersed over the brain vectorially. Our system was developed on the basis of the cortical structure of the brain cortex and the direction of the induced electric field. In order to verify the system accuracy, Motor Evoked Potentials (MEPs) elicited by TMS at the hand muscles innervated by the primary motor cortex (M1) were measured as electromyogram (EMG). And functional vectorial map of the excitability of M1 in the resting state was obtained by rotating the stimulation coil at a constant location.

Suppression of Electromyogram of Hand Muscle Elicited by Transcranial Magnetic Stimulation Over the Primary Motor Cortex

Cortical motor neuronal activation by transcranial magnetic stimulation (TMS) over the primary motor cortex area (M1) produces efferent signals that pass through the cortico-spinal tracts. As a result, motor evoked potentials (MEPs) are observed at muscles innervated by the stimulated motor neurons. It is well known that TMS can cause a silent period in the voluntary electromyogram (EMG). In the present study, TMS was applied to the Ml during thumb tapping. The influence of TMS on voluntary muscle contraction was discussed. Thumb trajectory was observed with a three-dimensional tracking device, and EMG of the abductor pollicis brevis (APB) muscle was also measured. The authors confirmed a change in thumb velocity in the downward direction during voluntary movement when TMS was applied, indicating that tissue excitation elicited by TMS causes loss of control of peripheral muscle motor control during voluntary movement.

Modification of Motor Evoked Potentials Caused by Electrical Peripheral Nerve Stimulation in Transcranial Magnetic Stimulation

Somatosensory cortex receives afferent inputs from skeletal muscles and joints while a voluntary movement is conducted. Although this sensory feedback may regulate the efferent motor control signals generated in the motor cortex, the relationship between the afferent sensory signals and the efferent motor signals is still unclear. In this study, we investigated the relationship between the afferent signals elicited by an electrical stimulus of a peripheral nerve and the efferent signals produced by a transcranial magnetic stimulation (TMS) of the motor cortex. The changes of motor evoked potentials (MEPs) elicited by TMS following an electrical stimulus of a median nerve were observed. The results showed that the MEPs were significantly attenuated when the inter-stimulus interval (ISI) between the electrical stimulus and the TMS was 20 ms, and that the MEPs were significantly enhanced when the ISI was longer than 35 ms. Furthermore, the brain condition which affected the MEPs was evaluated with the somatosensory evoked fields (SEFs) measured with magneto-encephalography (MEG). It was suggested that the activation and direction of the current dipole in the primary somatosensory cortex was related to the effect of the afferent signals on the motor function.

Noninvasive measurement of dynamic brain signals using light penetrating the brain

Conventional techniques for the noninvasive measurement of brain activity involve critical limitations in spatial or temporal resolution. Here, we propose the method for noninvasive brain function measurement with high spatiotemporal resolution using optical signals. We verified that diffused near-infrared light penetrating through the upper jaw and into the skull, which we term as optoencephalography (OEG), leads to the detection of dynamic brain signals that vary concurrently with the electrophysiological neural activity. We measured the OEG signals following the stimulation of the median nerve in common marmosets. The OEG signal response was tightly coupled with the electrophysiological response represented by the somatosensory evoked potential (SSEP). The OEG measurement is also shown to offer rather clear discrimination of brain signals.

Current Dipole Estimation in MEG by Spatial Interpolation of Magnetic Sensors

In this study, a method for current dipole estimation with spatial interpolation of measured magnetic fields in magnetoencephalogram (MEG) is proposed. This method applies virtual magnetic (M v ) sensors uniformly interpolated in the surface comprised of MEG (M r ) sensors. Orientations and output signals of the virtual magnetic sensors are calculated by a spatial linear interpolation based on those of real magnetic sensors. For determining an optimal value of regularization parameter (α) in minimum norm inverse solutions, M v sensors are divided into some groups randomly. Quantities of magnetic field (b k ) at the M r sensors are calculated by estimated dipoles with each group of M v sensors. α is determined by minimization of the total sum of differences between b k and the output signals measured by M r sensors. In order to confirm the validity of the proposed method, we estimated source distribution of N20m components of unilateral and bilateral somatosensory evoked fields (SEFs) measured by a 160-channel axial SQUID gradiometer system, when subject’s right and/or left median nerve was electrically stimulated. The proposed method was able to estimate source distribution in the primary somatosensory cortex (S1). Furthermore, the source distribution estimated by the proposed method tended to be more confined than that estimated by a cross validation error method. These results indicate that the virtually improved spatial resolution of MEG data can estimate more confined source distribution.

Effect of transcranial magnetic stimulation on force of finger pinch

Transcranial magnetic stimulation (TMS) is used to explore many aspects of brain function, and to treat neurological disorders. Cortical motor neuronal activation by TMS over the primary motor cortex (M1) produces efferent signals that pass through the corticospinal tracts. Motor-evoked potentials (MEPs) are observed in muscles innervated by the stimulated motor cortex. TMS can cause a silent period (SP) following MEP in voluntary electromyography (EMG). The present study examined the effects of TMS eliciting MEP and SP on the force of pinching using two fingers. Subjects pinched a wooden block with the thumb and index finger. TMS was applied to M1 during the pinch task. EMG of first dorsal interosseous muscles and pinch forces were measured. Force output increased after the TMS, and then oscillated. The results indicated that the motor control system to keep isotonic forces of the muscles participated in the finger pinch was disrupted by the TMS.

Disturbance on inhibitory control of reaching finger movement caused by transcranial magnetic stimulation

In the present report, we investigated the nature of the reaching finger movement after the stop signal accompanied with the transcranial magnetic stimulation (TMS) of the primary motor cortex (M1) in order to elucidate the temporal function of M1 for the inhibitory control of the voluntary finger movement. The go-stop task of the index finger movement, which consisted of the no-TMS task and the TMS task with various stop signal delay (SSD) ranged from 0 to 450 ms in intervals of 50 ms, was performed. In the no-TMS task: the task with the stop signal without the TMS, the finger movement was able be stopped prior to the target when the SSD was shorter than 250 ms, whereas the finger did not stop prior to the target when the SSD was 250 ms and longer. However, in the TMS task: the task with the TMS at the moment of the stop signal, the distance and velocity of the finger movement with the short SSD were not different from those with the long SSD. The results indicate that the TMS of the M1 disturbs the inhibitory function of the M1 independently from the pre-programmed voluntary movement.

Trajectory control model of finger movement after transcranial magnetic stimulation

s / Neuroscience Research 68S (2010) e109–e222 e147 P1-g08 GPR155 gene organization and expression in mouse brain Stefan Trifonov , Takeshi Houtani, Jun-ichi Shimizu, Yuji Yamashita, Satoko Hamada, Masahiko Kase, Masato Maruyama, Tetsuo Sugimoto Dept. of Anat. and Brain Sci., Kansai Medical University The important role of GPR155 in the brain is apparent from its significant dysregulation in the caudate nucleus of Huntington disease patients and animal models. GPR155 is also dysregulated in lymphoblastoid cells of humans with autism spectrum disorders. We report the structural organization of GPR155 gene and the generation of five variants of GPR155 mRNA. GPR155 is most probably a 17-TM membrane protein. Variant 1 and Variant 5 proteins have an intracellular, conserved DEP domain near the C-terminal. Further, we present the level of expression of GPR155 mRNA in different mouse tissues. The mRNAs for GPR155 are widely expressed in adult mouse tissues and during development. In situ hybridization was used to determine the distribution of GPR155 in mouse brain. The GPR155 mRNAs are widely distributed in forebrain regions and have more restricted distribution in the midbrain and hindbrain regions. The highest level of expression was in the lateral part of striatum and hippocampus. The expression pattern of GPR155 mRNAs in mouse striatum was very similar to the expression pattern of cannabinoid receptor type 1 (CB1) in rat. doi:10.1016/j.neures.2010.07.2224 P1-g09 An analysis of joint coordination for dampening hand vibration during human walking Shunta Togo , Takahiro Kagawa, Yoji Uno Dept Mechanical Science and Engineering, Nagoya Univ, Nagoya Carrying a cup without spilling water is one of dexterous tasks. If the hand is vibrating in walking, the water spills out of the cup. We conjecture that the human coordinate some body parts to dampen hand vibration in the task. UCM analysis has been used to quantify the coordination of human movements. UCM analysis divides the variance of motor elements with redundancy on a performance variable into two orthogonal components; 1) subspace of structure of motor elements that does not affect the performance variable (UCM), and 2) subspace of structure of motor elements orthogonal to UCM that directly affects (ORT). If a particular performance variable is controlled by the coordination of motor elements, ORT component will be smaller and UCM component will be larger. Here we hypothesize that reducing hand-jerk and keeping cup angle constant by coordinating joint movements are required to achieve the task. We measured human movements in carrying a cup with water or without water by a three-dimensional position measurement system and analyzed joint coordination by using UCM analysis. It was empirically confirmed that the hand-jerk and variance of cup-angle with water of all subjects were significantly smaller than those without water especially at the time of peak. For cup-angle, ORT component was smaller and UCM component was larger in carrying a cup with water as expected. However, those components of hand-jerk were contrary to our expectation. The point is that UCM component was significantly larger than ORT component in carrying a cup with water for both cup-angle and handjerk. These results suggest that the human reduces hand jerk and keeps cup angle constant by coordinating joint movements to dampen hand vibration in carrying a cup with water. In addition, we investigated the effect of human vision for dampening hand vibration. doi:10.1016/j.neures.2010.07.2225 P1-g10 Crosstalk in implicit assignment of visual movement error during bimanual motor learning Shoko Moriyama , Daichi Nozaki Graduate School of Education, The University of Tokyo The brain constructs a neural controller called “internal model” to perform a desired movement. In the learning process, the movement error (i.e., consequence) needs to be appropriately associated with the output of the controller (i.e., action). However, their association is not necessarily guaranteed for bimanual movement in which two distinct actions by both arms result in two movement errors. Considering implicit nature of the motor learning process, the movement error of left (or right) arm can be erroneously associated with the output of right (or left) arm controller. Here we investigate how the brain assigns the movement error of each arm to each action.Participants performed bimanual symmetric back-and-forth movements. Only the position of the right hand was presented by a cursor on a horizontal screen (i.e., left hand was invisible) either at the right or left side of the body. They knew explicitly that the cursor reflected the right hand movement. In a training session, gradually increasing clockwise rotation was applied to the cursor position around the starting position (0–45 deg; 0.6 deg/trial increment). Due to the gradual increment, they were unaware of the presence of rotation throughout the session.The movement direction of the right hand was gradually rotated counter-clockwise, indicating that the right hand adapted to the rotation. Such gradual rotation was also observed for the left hand (though it was smaller than for the right hand), especially when the cursor was presented on the left side. Thus, the visual movement error of the right hand presented at the left side of the body was implicitly assigned to the left arm movement controller. Additional experiments in which 2 cursors were presented show that the adaptation was impaired when the rotations were opposite as compared to when they were the same directions. These results indicate the presence of crosstalk in association between action and consequence in bimanual movement learning. doi:10.1016/j.neures.2010.07.2226 P1-g11 Trajectory control model of finger movement after transcranial magnetic stimulation Osamu Hiwaki , Masato Odagaki, Hiroshi Fukuda Graduate School of Information Sciences, Hiroshima City University, Hiroshima We investigated trajectory control in voluntary finger stabilization against the external force after transcranial magnetic stimulation (TMS) of primary motor cortex (M1). We first measured a trajectory of the index finger in the task that a subject stabilized the index finger with loading the external force on the finger-tip accompanied by the TMS of the contralateral M1. The subject was required to keep the index finger at constant position with balancing against the external force, which was loaded on the finger-tip with the haptic device, in extension direction. The metacarpophalangeal (MP) joint was solely allowed to flex and extend with fixation of the two other joints of the index finger. The subject was asked to return the index finger to the initial position voluntarily after the twitch caused by the TMS. The trajectory of the finger-tip was measured with the haptic device, and the EMG at first dorsal interosseus (FDI) muscle was monitored simultaneously. The observed trajectory was as follows: the finger started to flex 50 ms after the TMS, and turned to extension at the latency of 180 ms followed by the peak of extension at the latency of 334 ms, thereafter returned to the initial position. We tried to explain the control mechanism of the fingertip trajectory after the TMS by a dynamics model of the index finger. The index finger was modeled as a one-link rigid-body rotating around a hinge joint. Before the TMS, feedback control which balanced the voluntary torque of MP joint against the external force was modeled. The TMS evoked the involuntary torque of the MP joint, and interrupted the feedback control during the SP. After the SP, the feedback control which returned the finger to the initial position was recovered. The finger trajectory delineated with the model corresponded to the measured trajectory. The proposed model successfully reproduced the observed trajectory in the stabilizing task for the index finger after the TMS of M1. doi:10.1016/j.neures.2010.07.2227 P1-g12 Trajectory formation of voluntary human thumb movement with minimum torque change model Hiroshi Fukuda , Masato Odagaki, Osamu Hiwaki Graduate School of Information Sciences, Hiroshima City University, Hiroshima In the present study, trajectories of the voluntary point-to-point thumb movement were measured and analyzed based on the minimum torque change model (MTCM). Subject’s thumb-tip was inserted into the thimble at the end of a parallel-link manipulator. The subject was instructed to perform point-to-point movements with the thumb as fast and precisely as possible, which were achieved by moving the metacarpophalangeal (MP) and interphalangeal (IP) joints. The thumb movement was restricted within the horizontal plane with the parallel-link manipulator. The position and velocity of the thumb-tip were measured using the parallel-link manipulator with 1 kHz of sampling frequency. After sufficient training of the point-to-point movement, 20 trials of the movement were measured.

Neural network for confirmation of coil location in transcranial magnetic stimulation by motor evoked potential and force

We proposed an artificial neural network to confirm the location of stimulating coil in transcranial magnetic stimulation (TMS) from data of finger force and electromyography (EMG). In experiments, finger forces of the right index finger and motor evoked potentials (MEPs) of the muscles involved in the generation of the finger forces were measured when the primary motor cortex in the left hemisphere of the cerebrum was stimulated by TMS. The measured finger forces and MEPs varied trial by trial although the stimulating coil and subjects head were fixed. The neural network learned the mapping from the MEPs and/or the finger forces to the coil location. After sufficient learning, the neural network was able to classify unlearned MEPs and finger forces into corresponding coil locations.