Toshio Soma

Neuromagnetic activation of primary and secondary somatosensory cortex following tactile-on and tactile-off stimulation

OBJECTIVE Magnetoencephalography (MEG) recordings were performed to investigate the cortical activation following tactile-on and tactile-off stimulation. METHODS We used a 306-ch whole-head MEG system and a tactile stimulator driven by a piezoelectric actuator. Tactile stimuli were applied to the tip of right index finger. The interstimulus interval was set at 2000 ms, which included a constant stimulus of 1000 ms duration. RESULTS Prominent somatosensory evoked magnetic fields were recorded from the contralateral hemisphere at 57.5 ms and 133.0 ms after the onset of tactile-on stimulation and at 58.2 ms and 138.5 ms after the onset of tactile-off stimulation. All corresponding equivalent current dipoles (ECDs) were located in the primary somatosensory cortex (SI). Moreover, long-latency responses (168.7 ms after tactile-on stimulation, 169.8 ms after tactile-off stimulation) were detected from the ipsilateral hemisphere. The ECDs of these signals were identified in the secondary somatosensory cortex (SII). CONCLUSIONS The somatosensory evoked magnetic fields waveforms elicited by the two tactile stimuli (tactile-on and tactile-off stimuli) with a mechanical stimulator were strikingly similar. These mechanical stimuli elicited both contralateral SI and ipsilateral SII activities. SIGNIFICANCE Tactile stimulation with a mechanical stimulator provides new possibilities for experimental designs in studies of the human mechanoreceptor system.

Cortical neuromagnetic activation accompanying two types of voluntary finger extension

We examined the amplitude and latency of movement-related cerebral field (MRCF) waveforms, the generator and afferent feedback of movement-evoked field 1 (MEF1), and the relationship between motor field neuromagnetic activity and electromyographic activity during performance of two types of voluntary index extension. Eight healthy, right-handed male volunteers participated in this study. Experiments for each subject consisted of recording of MRCFs following two types of finger movement. One (Task 1) involved voluntary extension of the right index finger to about 40 degrees . In the second (Task 2), an elastic band was placed on the right index fingertip, producing a resistance of about 1.5 times the electromyographic activity associated with the voluntary movement yielding extension to approximately 40 degrees . Peak amplitude and the ECD moment of the motor field differed significantly between the two tasks. In Task 2, the electromechanical delay from EMG onset to movement onset (77.8+/-16.2) was longer than in Task 1 (44.4+/-10.4). However, the latency from EMG onset to MEF1 peak was 87.6+/-8.5 ms in Task 2, and did not differ significantly from that in Task 1 (88.6+/-8.5). The ECDs of MEF1 were located significantly medial to N20 m and lateral and posterior to the motor field. These findings suggest that the ECD of MEF1 is located in area 3b, but is slightly different from N20 m, and that this MEF1 component activation is due not to the onset of joint movement but to that of muscular contraction.

Muscle-afferent projection to the sensorimotor cortex after voluntary movement and motor-point stimulation: An MEG study

OBJECTIVE To investigate the projection of muscle afferents to the sensorimotor cortex after voluntary finger movement by using magnetoencephalography (MEG). METHODS The movement-evoked magnetic fields (MEFs) after voluntary index-finger extension were recorded by a 204-channel whole-head MEG system. Somatosensory-evoked magnetic fields (SEFs) were recorded after motor-point stimulation was applied to the right extensor indicis muscle by using a pair of wire electrodes. RESULTS The MEF waveforms were observed at 35.8±9.7 ms after movement onset (MEF1). The most concentrated SEFs were identified at 78.7±5.6 ms (M70), and the onset latency of M70 was 39.0±5.5 ms after motor-point stimulation. The mean locations of the equivalent current dipoles (ECDs) of MEF1 and M70 were significantly medial and superior to that of N20m elicited by median-nerve stimulation. The ECD locations and directions of both MEF1 and M70 were concordant in the axial, coronal and sagittal planes. CONCLUSIONS MEF1 and M70 might be elicited by muscle-afferent feedback following muscle contraction. In addition, these ECDs may be located in area 4. SIGNIFICANCE Motor-point stimulation is a useful tool for confirming the projection of muscle-afferent feedback to the sensorimotor cortex after voluntary movement.

Effect of warm-up exercise on delayed-onset muscle soreness

Abstract In this study, we wished to determine whether a warm-up exercise consisting of 100 submaximal concentric contractions would attenuate delayed-onset muscle soreness and decreases in muscle strength associated with eccentric exercise-induced muscle damage. Ten male students performed two bouts of an elbow flexor exercise consisting of 12 maximal eccentric contractions with a warm-up exercise for one arm (warm-up) and without warm-up for the other arm (control) in a randomized, counterbalanced order separated by 4 weeks. Muscle temperature of the biceps brachii prior to the exercise was compared between the arms, and muscle activity of the biceps brachii during the exercise was assessed by surface integral electromyogram (iEMG). Changes in visual analogue scale for muscle soreness and maximal voluntary isometric contraction strength (MVC) of the elbow flexors were assessed before, immediately after, and every 24 h for 5 days following exercise, and compared between the warm-up and control conditions by a two-way repeated-measures analysis of variance. The pre-exercise biceps brachii muscle temperature was significantly (P<0.01) higher for the warm-up (35.8±0.2°C) than the control condition (34.4±0.2°C), but no significant differences in iEMG and torque produced during exercise were evident between conditions. Changes in muscle soreness and MVC were not significantly different between conditions, although these variables showed significant (P<0.05) changes over time. It was concluded that the warm-up exercise was not effective in mitigating delayed-onset muscle soreness and loss of muscle strength following maximal eccentric exercise.

S18.3 Cortical neuromagnetic activation following passive and active finger movement

Introduction: Our experimental goal is to examine the sensory feedback from periphery following voluntary movement. We have reported that the first component of the movement evoked cortical magnetic fields (MEF) was due not to joint movement but to that of muscular contraction (Clin Neurophysiol, 2010). However, the reasons of the long latency after electromyographic onset are not fully understood. Objectives: MEG study with passive finger movement was performed to investigate the neural mechanisms following voluntary finger movement. Methods: Six healthy male subjects (mean age 36.5±8.9 years) participated in this study. All subjects had given their written informed consent, and the study was approved by the ethics committee at our university. For MEG measurement, we used a 306 ch whole-head MEG system (Neuromag, Elekta, Finland). MEG signals were sampled at 1000 Hz with band-pass filtering from 0.03 to 330 Hz. All participants performed voluntary index extension to record the movement related cortical magnetic fields (MRCFs) and were underwent passive index extension to record the somatosensory evoked magnetic fields (SEFs). The sources of the components of interest in the MEF and SEF were estimated as the equivalent current dipoles (ECD). Results: We clearly confirmed the MRCF and SEF waveforms at the sensorimotor area contralateral to the movement in all subjects. The most prominent MRCF waveform was MEF1, which was observed at 30.1±4.8 ms after movement onset. On the other hand, the most concentrated SEF peak was identified at 37.6±8.0 ms after the onset of passive movement. The mean ECD locations for MEF1 were significantly medial to N20m after median nerve stimulation. However, the ECD locations of the first component after passive movement were very similar to the N20m. Conclusions: The MEF1 after voluntary movement were different response from the first component following passive movement in location of the ECDs. These results suggest that MEF1 was not elicited by the cutaneous receptor or joint receptor.

P33-11 Influence of movement practice on movement-related cortical fields

current dipoles at 1 ms steps using individual spherical head models. Sources were then superimposed on the coregistered structural MRIs. Results: Statistically significant CKC was evident in all ten subjects at 1.5 4.5 Hz and 3 9 Hz, corresponding to hand kinematics. Coherence values ranged from 0.164 to 0.788. In the no-touch condition, clusters of sources were mostly located at the contralateral primary motor (M1) cortex, while in the touch condition they were both at contralateral primary somatosensory (SI) and M1 cortices. Conclusions: Voluntary movements can be monitored during MEG recordings with an accelerometer. The coherence between the accelerometer and the MEG signals reveals activations of M1 and S1 cortices. Acknowledgments: Brains Back to Brussels grant (VJ) by the Institut d’Encouragement de la Recherche Scientifique et de l’Innovation de Bruxelles (Brussels, Belgium), ERC Advanced Grant #232946, and FRS-FNRS (Fonds de la Recherche Scientifique, Belgium; Chercheur scientifique logistique (MB)) for the financial support. Helge Kainulainen and Ronny Schreiber at the Brain Research Unit for the technical support.