Satoshi Shibuya

Influence of skin blood flow on near-infrared spectroscopy signals measured on the forehead during a verbal fluency task.

Brain activity during a verbal fluency task (VFT) has been the target of many functional imaging studies. Most studies using near-infrared spectroscopy (NIRS) have reported major activation in the frontal pole, but those using PET or fMRI have not. This led us to hypothesize that changes in the NIRS signals measured in the forehead during VFT were due to changes in skin blood flow. To test this hypothesis, we measured NIRS signals and the Doppler tissue blood flow signals in the foreheads of 50 participants. The measurements were performed while each participant produced words during two 60-s periods with an interval of 100 s. In addition to a conventional optode separation distance of 30 mm (FAR channels), we used a short distance--5mm (NEAR channels)--to measure NIRS signals that originated exclusively from surface tissues. The oxygenated hemoglobin (oxyHb) concentration in the FAR and NEAR channels, as well as the Doppler blood flow signal, increased in a similar manner during the two periods of word production; the signal increase in the first period was twice as high as that in the second period. Accordingly, the mean changes in oxyHb concentration in the FAR channels were correlated closely with the changes in the NEAR channels (R(2) = 0.91) and with the integrated Doppler skin blood flow signal (R(2) = 0.94). Furthermore, task-related NIRS responses disappeared when we blocked skin blood flows by pressing a small area that covered a pair of optodes. Additionally, changes in the FAR channel signals were correlated closely with the magnitude of pulsatile waves in the Doppler signal (R(2) = 0.92), but these signals were not highly correlated with the pulse rate (R(2) = 0.43). These results suggest that a major part of the task-related changes in the oxyHb concentration in the forehead is due to task-related changes in the skin blood flow, which is under different autonomic control than heart rate.

Reassessment of non-monosynaptic excitation from the motor cortex to motoneurons in single motor units of the human biceps brachii

Corticospinal excitation is mediated by polysynaptic pathways in several vertebrates, including dexterous monkeys. However, indirect non-monosynaptic excitation has not been clearly observed following transcranial electrical stimulation (TES) or cervicomedullary stimulation (CMS) in humans. The present study evaluated indirect motor pathways in normal human subjects by recording the activities of single motor units (MUs) in the biceps brachii (BB) muscle. The pyramidal tract was stimulated with weak TES, CMS, and transcranial magnetic stimulation (TMS) contralateral to the recording side. During tasks involving weak co-contraction of the BB and hand muscles, all stimulation methods activated MUs with short latencies. Peristimulus time histograms (PSTHs) showed that responses with similar durations were induced by TES (1.9 ± 1.4 ms) and CMS (2.0 ± 1.4 ms), and these responses often showed multiple peaks with the PSTH peak having a long duration (65.3% and 44.9%, respectively). Such long-duration excitatory responses with multiple peaks were rarely observed in the finger muscles following TES or in the BB following stimulation of the Ia fibers. The responses obtained with TES were compared in the same 14 BB MUs during the co-contraction and isolated BB contraction tasks. Eleven and three units, respectively, exhibited activation with multiple peaks during the two tasks. In order to determine the dispersion effects on the axon conduction velocities (CVs) and synaptic noise, a simulation study that was comparable to the TES experiments was performed with a biologically plausible neuromuscular model. When the model included the monosynaptic-pyramidal tract, multiple peaks were obtained in about 34.5% of the motoneurons (MNs). The experimental and simulation results indicated the existence of task-dependent disparate inputs from the pyramidal tract to the MNs of the upper limb. These results suggested that intercalated interneurons are present in the spinal cord and that these interneurons might be equivalent to those identified in animal experiments.

Functional assessment of proximal arm muscles by target-reaching movements in patients with cervical myelopathy

BACKGROUND CONTEXT In animal studies, distal and proximal arm movements are differently affected by spinal pyramidotomy because of the contributions of spinal interneuronal systems. In animals, interneuronal systems are also suggested to contribute to the recovery of dexterous hand movements. However, no clinical tests to evaluate proximal arm movements and functions of interneuronal systems have been described. PURPOSE To compare parameters from proximal arm movements between patients and controls and in patients before and after decompression surgery. STUDY DESIGN A cross-sectional and longitudinal study performed at Kyorin University School of Medicine, Japan. PATIENT SAMPLE Patients with clinical features of cervical spondylotic myelopathy, without coexisting neurological abnormality. METHODS Twenty-eight patients and 15 age-matched controls performed reach-to-touch movements. Analysis of these movements identified several parameters, including time for online correction (correction time) induced by sudden target jump. Parameters were compared with scores from conventional tests, such as Japanese Orthopedic Association (JOA) score, 10-second grip-and-release test, manual muscle testing, and motor-evoked potential. RESULTS Preoperatively, patients showed long correction time and variable touch position, neither of which correlated with any scores from conventional tests. Reaching parameters recovered markedly immediately after decompression surgery, whereas conventional scores, which mainly assess hand functions, recovered much more slowly. Correction time and JOA score showed correlations when postoperative data were included, and long-term recovery of JOA score was more predictable with the inclusion of data for correction times from before and immediately after surgery. CONCLUSION Analysis of arm movements is useful to evaluate symptoms and predict recovery of hand functions after surgery in patients with cervical myelopathy. These results suggest the importance of interneuronal systems, in addition to the pyramidal tract, for motor control even in humans.

Spontaneous imitative movements induced by an illusory embodied fake hand

ABSTRACT In the rubber hand illusion (RHI), individuals perceive a fake hand as their own when the hidden real hand and visible fake hand are synchronously stroked. Several RHI studies have reported that visual manipulation of the embodied fake hand inversely affects the perceptual processing of the observers own hand (e.g., thermal or pain sensitivity). In this study, we examined whether motor manipulation of the fake hand similarly affects the observers motor system. Our study employed a novel RHI paradigm wherein stroking was interrupted by unexpected movement of the fake hand (i.e., finger spreading) while measuring electroencephalography (EEG). We found that participants often spontaneously moved their hands in accordance with the movement of the fake hand only in the RHI (synchronous) sessions. EEG analyses revealed enhanced neural activation (mu‐rhythm desynchronization) of the motor system during observation of the fake hand movement. Moreover, motor activation was greater in the synchronous than in the asynchronous condition and significantly correlated with the feeling of body ownership over the fake hand. These findings provide strong behavioral and neurophysiological evidence of ‘motor back projection’, in which the movement of an illusory embodied body part is inversely transferred to the sensorimotor system of the observer. HIGHLIGHTSWhen an illusory embodied fake hand moved unexpectedly, subjects often elicited spontaneous and imitative hand movements.EEG analysis found enhanced the motor system activation during observation of the embodied fake hand movement.Magnitude of the motor system activation significantly correlated with feelings of body ownership toward the fake hand.

Hand Dexterity Impairment in Patients with Cervical Myelopathy: A New Quantitative Assessment Using a Natural Prehension Movement

Cervical myelopathy (CM) caused by spinal cord compression can lead to reduced hand dexterity. However, except for the 10 sec grip-and-release test, there is no objective assessment system for hand dexterity in patients with CM. Therefore, we evaluated the hand dexterity impairment of patients with CM objectively by asking them to perform a natural prehension movement. Twenty-three patients with CM and 30 age-matched controls were asked to reach for and grasp a small object with their right thumb and index finger and to subsequently lift and hold it. To examine the effects of tactile afferents from the fingers, objects with surface materials of differing textures (silk, suede, and sandpaper) were used. All patients also underwent the Japanese Orthopedic Association (JOA) test. Preoperative patients showed significantly greater grip aperture during reach-to-grasp movements and weaker grip force than controls only while attempting to lift the most slippery object (silk). Patients, immediately after surgery, (n = 15) tended to show improvements in the JOA score and in reaction time and movement time with respect to reaching movements. Multiple regression analysis demonstrated that some parameters of the prehension task could successfully predict subjective evaluations of dexterous hand movements based on JOA scores. These results suggest that quantitative assessments using prehension movements could be useful to objectively evaluate hand dexterity impairment in patients with CM.

Development of VR platform for cloud-based neurorehabilitation and its application to research on sense of agency and ownership

Graphical Abstract Abstract Recently, neurorehabilitation that uses virtual reality systems is being applied in clinical settings to deal with issues such as phantom limb pain (PLP) as an alternative to mirror box therapy. One of the weak points of mirror box therapy is that the desired analgesia effect might not be confirmed in some patients. One hypothesis to explain this phenomenon is that the subjective sense of the length of a phantom limb is different from that of an intact limb. Since the gap between body representation in the brain and actual sensory feedback is considered one of the causes of PLP, different lengths of a subjective phantom limb are a serious problem for mirror box therapy and similar VR-based rehabilitation methods. We are thus developing a VR system that displays an avatar that has the same length as the subjective phantom limb. The purpose of the current study is to determine the feasibility of the VR system – specifically, whether it has enough effect on sense of agency (SoA) and sense of ownership (SoO) for healthy subjects – before conducting experiments for actual phantom limb patients. To this end, we developed a VR system in which a virtual avatar performs a motion identical to that of the subject by means of a motion capturing device (Kinect V2). The subject wears a 3D head mounted display (Oculus Rift DK2) to experience seeing through the eyes of the avatar. Six conditions of avatar representation were used: two appearances of a normal human arm and a robot arm and three lengths of the arm (short, medium, and long). The subject executes elbow flexion-extension movement of the right arm, which causes the same movement in the VR avatar’s arm. After the induction movement, the subjective sense of the length of the right arm is measured by a pointing gesture of the left hand. Twelve subjects participated in this experiment. Results showed that the subjective length of the arm was changed according to the length of the displayed arm in the VR environment. From the results of a questionnaire, we found that there is no negative effect on SoA. SoO when the subjects watch the natural human avatar is stronger than when the robot arm is shown. These results are positive, thus confirming the basic potential of the proposed VR system. In conclusion, the change of self-body appearance of a VR avatar has enough effect on subjective sense of arm length. Since the subjective sense of arm length is strongly related to body representation in the brain, we believe that the system can be a platform for research on embodied-brain science systems.

Evaluating effect of sense of ownership and sense of agency on body representation change of human upper limb

To improve rehabilitation of the diseases which are caused by the mismatch between real body and body representation, it is necessary to understand the mechanism of body representation change. It is assumed that sense of agency and sense of ownership are closely-related with body representation and influence body representation change of the body parts without visual information. We focused on human upper limb and performed experiment with participants on four condition related to sensitivity of agency and ownership. We measure perceived position change of elbow and finger by pointing judgement using motion capture. Visual stimulation which participants given is only virtual hand. Our experiment has revealed that sense of agency influence the body representation change on the body parts which is invisible to participants.

Functional assessment of patients with cervical myelopathy by using target-reaching movements

Large cholinergic synaptic boutons named “C-terminals” contact the somata and proximal dendrites of motoneurons. In the spinal cord, C-terminals derive from cholinergic interneurons in the medial layer VII and regulate the motoneuron excitability via the activation of muscarinic receptors. We have previously identified that neurons in the magnocellular reticular formation in the medulla oblongata are the origins of the C-terminals in the hypoglossal nucleus, which is considered as the rostral extension of spinal motor columns. The projection patterns of the C-terminals are thus well conserved in the somatic motor neurons throughout spinal cord and caudal brainstem. In the cranial motor nuclei, the motoneurons that innervate skeletal muscles comprise two subtypes: branchiomotor and somatic motor neurons. The distinct differentiation between these two subtypes implies that the axonal projections and molecular profiles in the original neurons of the C-terminals are different in each subtype. However, the neural source of the C-terminals in branchiomotor nuclei remains unknown. To address this question, we explored the origin of the C-terminals in the branchiomotor nuclei by using the anterograde tract tracing techniques combined with immunohistochemistry of vesicular acetylcholine transporter as a specific marker for cholinergic terminals. After injections of biotinylated dextran amine (BDA) into the pontine, intermediate and gigantocellular reticular nuclei, double-labeled large terminals were observed in close apposition to the somata of motoneurons in the trigeminal and facial nuclei. These findings suggest that C-terminals in branchiomotor nuclei have similar organization of cells of origin to those in the somatic motor nuclei. We will also discuss the expression of the molecular markers of cholinergic neuron in the identified origins of the C-terminals.

P31-17 Analysis of the target-reaching movement in patients with cervical myelopathy

Objective: In animal studies, it is shown that proximal (target-reaching) and distal (grasping) movements of the upper extremity are differently affected by spinal pyramidotomy. We analyzed the target-reaching movement in patients with cervical myelopathy, and examined if it is useful to evaluate symptoms, and to predict recovery after the decompression surgery. Methods: Twenty-eight pre-operative patients and 15 age-matched controls participated in the experiments. Some patients returned to the experiments, up to 1 year after the surgery. They performed targetreaching movements, cued by sound. Three-dimensional positions of the index finger were sampled by an electromagnetic motion tracking system. By analyzing the movement, reaction time, movement time and accuracy of touch position (TP) were obtained, as well as time for online correction (CT) induced by sudden target jump. The parameters were compared with scores of conventional tests; the JOA score, 10-second grip and release test, the manual muscle testing, and motor evoked potential induced by transcranial magnetic stimulation of the motor cortex. Results: All patients mainly claimed clumsiness in the hand movement pre-operatively, and showed significantly deteriorated scores in conventional tests. They also showed poor online adjustments of the reaching movement. It was reflected in long CT and variable TP, though the other parameters were not affected significantly. However, CT was not correlated with any score from conventional tests. After the surgery, CT immediately returned to the normal level, while the JOA score, which mainly evaluate hand functions, improved gradually during months. When including post-operative data, CT and JOA score were correlated, and recovery of the latter could be predicted better if including CT immediately after the surgery. Conclusions: The target-reaching movement is useful to evaluate deficits that cannot be detected by conventional tests. Post-operative JOA score suggests that recovery in hand functions partly depends on mechanisms for the reaching movement.

Premotor attentional shift under virtual environments

Current knowledge on the brain activity time course in motor tasks is mainly based on single unit recordings, so that global evaluation is difficult. We obtained MEG and fMRI data during directed wrist movement and combined them in a hierarchical Bayesian method in order to estimate the cortical currents over the whole brain. This procedure is non-invasive and reveals brain activity in spatial as well as temporal detail. Brain vertices with time courses exceeding a certain threshold were spatially clustered. The average time course of each cluster was plotted and the time course peaks investigated with respect to their sequence in time. During the planning period the first activation peak is observed in the right parietal cortex spreading to other areas in the parietal and temporal cortex areas. This activity is followed by activation in sensorimotor areas. During movement preparation a slow rise of activation is observed in sensorimotor areas followed by more sudden activation in the parietal cortex right after movement onset.