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The present study investigated the effects of hypocapnia and hypercapnia on human somatosensory processing by utilizing somatosensory evoked magnetic fields (SEFs) with magnetoencephalography (MEG). Thirteen volunteers participated in two experiments separately to measure respiratory and cardiovascular data and SEFs. Both experiments consisted of a combination of normal and rapid respiratory rhythms and two inspiratory gas conditions (air and a hypercapnic gas); normal breathing with air (NB), rapid breathing with air (RB), normal breathing with the hypercapnic gas (NB+Gas), and rapid breathing with gas (RB+Gas). Partial pressures of end-tidal CO 2 (P ETCO2) increased during inhaling the hypercapnic gas and decreased during RB, but the RB+Gas condition continued to cause elevated PETCO 2 compared with the baseline. Subsequently, middle cerebral artery blood (MCA) velocity using transcranial Doppler changed as well, while mean MCA velocity increased under the RB+Gas condition. The peak amplitude of the M60 component in SEFs was also significantly larger under with-gas than without-gas conditions, irrespective of the respiratory frequency. These results suggest that there is a close relationship between cerebral blood flow and neural activity of the M60 component in SEFs. This study provides evidence to further understanding on one of the neural mechanisms of hypercapnia. • We investigated effects of hypocapnia and hypercapnia on somatosensory processing. • Middle cerebral artery blood velocity increased under with-gas conditions. • The peak amplitude of the M60 component also increased under with-gas conditions. [ABSTRACT FROM AUTHOR]

Magnetoencephalography is primarily sensitive to current sources tangential to the skull. Therefore, currents generated in area 3b of the primary somatosensory cortex (S1) and area 4 of primary motor cortex (M1) located on the posterior and anterior banks of the central sulcus, respectively, are easily detected. The movement-related cortical magnetic fields (MRCFs) following voluntary movement and the somatosensory magnetic fields (SEFs) generated by peripheral mixed nerve stimulation (e.g., median nerve) have been widely used to investigate the physiology of normal somatosensory cortical processing. Here, we describe the MRCFs produced by two types of movement (experiment 1) and the SEFs elicited by motor point stimulation (experiment 2), passive movement (experiments 3 and 4), and mechanical stimulation (experiments 5, 6, and 7). In addition, we examined the modulation of these fields.

Abstract: Magnetoencephalography (MEG) recordings were collected to investigate the effect of the number of mechanical pins and inter-pin distance on somatosensory evoked magnetic fields (SEFs) following mechanical stimulation (MS). We used a 306-ch whole-head MEG system. SEFs were elicited through tactile stimuli with 1-, 2-, 3-, 4- and 8-pins using healthy participants. Tactile stimuli were applied to the tip of the right index finger. SEF following electrical stimulation of the index finger was recorded in order to compare the activity in the primary somatosensory cortex (S1) following MS. Prominent SEFs were recorded from the contralateral hemisphere approximately 54ms (P50m) and 125ms (P100m) after MS regardless of the number of pins. Equivalent current dipoles were located in the S1. The source activities for P50m and P100m significantly increased in tandem with the number of pins for MS. However, the increased ratios for the source activities according to the increase in the number of pins were significantly smaller than that induced by electrical stimulation, and when the number of the pins doubled from 1-pin to 2-pins, from 2-pins to 4-pins, and from 4-pins to 8-pins, S1 activities increased by only 130%. Additionally, source activities significantly increased when the inter-pin distance increased from 2.4 to 7.2mm. The number of stimulated receptors was considered to have increased with an increase in the inter-pin distance as well as an increase in the number of pins. These findings clarified the effect of the number of pins and inter-pin distance for MS on SEFs. [Copyright &y& Elsevier]

Abstract: Children with cerebral palsy (CP) have altered tactile, proprioceptive and kinesthetic awareness. These sensory impairments appear to be related to an aberrant organization of the somatosensory cortex. To date, the neuromagnetic responses of somatosensory cortices representing the foot have not been investigated in children with spastic diplegic CP. In this investigation, we used magnetoencephalography (MEG) to evaluate cortical differences in the earliest somatosensory responses elicited by foot stimulation in typically developing children and those with spastic diplegic CP who have a Gross Motor Function Classification Score of III–IV. All participants underwent unilateral tibial nerve stimulation of each foot as whole brain MEG data were acquired. Primary somatosensory cortical responses were modeled using an equivalent current dipole for each foot. The results presented in this study are the first to show that activation of the somatosensory cortices representing the foot in children with spastic diplegic CP is diminished, but not latent. [ABSTRACT FROM AUTHOR]

Abstract: 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 2000ms, which included a constant stimulus of 1000ms duration. Results: Prominent somatosensory evoked magnetic fields were recorded from the contralateral hemisphere at 57.5ms and 133.0ms after the onset of tactile-on stimulation and at 58.2ms and 138.5ms 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 (168.7ms after tactile-on stimulation, 169.8ms 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. [Copyright &y& Elsevier]

Abstract: To obtain a direct sensorimotor integration assessment in primary hand cortical areas (M1) of patients suffering from focal task-specific hand dystonia, magnetoencephalographic (MEG) and opponens pollicis electromyographic (EMG) activities were acquired during a motor task expressly chosen not to induce dystonic movements in our patients, to disentangle abnormalities indicating a possible substrate on which dystonia develops. A simple isometric contraction was performed either alone or in combination with median nerve stimulation, i.e. when a non-physiological sensory inflow was overlapping with the physiological feedback. As control condition, median nerve stimulation was also performed at rest. The task was performed bilaterally both in eight patients and in 16 healthy volunteers. In comparison with results in controls we found that in dystonic patients: i) MEG-EMG coherence was higher; ii) it reduced much less during galvanic stimulation in the hemisphere contralateral to the dystonic arm, simultaneously with iii) stronger inhibition of the sensory areas responsiveness due to movement; iv) the cortical component including contributions from sensory inhibitory and motor structures was reduced and v) much more inhibited during movement. It is documented that a simultaneous cortico-muscular coherence increase occurs in presence of a reduced M1 responsiveness to the inflow from the sensory regions. This could indicate an unbalance of the fronto-parietal functional impact on M1, with a weakening of the parietal components. Concurrently, signs of a less differentiated sensory hand representation—possibly due to impaired inhibitory mechanisms efficiency—and signs of a reduced repertoire of voluntary motor control strategies were found. [Copyright &y& Elsevier]

Abstract: Movement control requires continuous and reciprocal exchange of information between activities of motor areas involved in the task program execution and those elaborating proprioceptive sensory information. Our aim was to investigate the sensorimotor interactions in the region dedicated to hand control in healthy humans, focusing onto primary sensory and motor cortices, by selecting the time window at very early latencies. Through magnetoencephalographic recordings, we obtained a simultaneous assessment of sensory cortex activity modulation due to movement and of motor cortex activity modulation due to sensory stimulation, by eliciting a galvanic stimulation to the nerve (the median nerve) innervating a muscle (the opponens pollicis), at rest or during voluntary contraction. The primary sensory and motor cortices activities were investigated respectively through excitability in response to sensory stimulation and the cortico-muscular coherence. The task was performed bilaterally. A clear reduction of the cortico-muscular coherence was found in the short time window following stimuli (between around 150–450 ms). In the same time period, the motor control of isometric contraction was preserved. This could suggest that cortical component of voluntary movement control was transiently mediated by neuronal firing rate tuning more than by cortico-muscular synchronization. In addition to the known primary sensory cortex inhibition due to movement, a more evident reduction was found for the component known to include a contribution from primary motor areas. Gating effects were lower in the dominant left hemisphere, suggesting that sensorimotor areas dominant for hand control benefit of narrowing down gating effects. [Copyright &y& Elsevier]

Abstract: Objective: To investigate the somatotopic organization of the facial skin area in the secondary somatosensory cortex (SII) in humans. Methods: Somatosensory evoked magnetic fields following air-puff stimulation of 5 body sites, the foot, the lip and 3 points of the facial skin (forehead, cheek and mandibular angle point), were recorded. We focused on activities in SII following stimulation of these 5 sites and compared dipole locations among them. Results: There was a clear somatotopic organization in SII with lip in the most lateral area, foot in the most medial area and face in an intermediate area close to the lip area. However, there was no significant difference of dipole localization in SII among the 3 areas of facial skin, similar to the overlapped somatotopic organization of facial skin areas in the primary somatosensory cortex in our previous study. Conclusions: The facial skin areas are considered to occupy a small area in SII with insufficient spatial separation to differentiate each area of facial skin even using magnetoencephalography which has a high spatial resolution. Significance: This is the first systematic study of the activated regions in SII following stimulation of the facial skin. [Copyright &y& Elsevier]

We recorded somatosensory evoked magnetic field (SEF) to investigate the differentiation in the receptive area for the face, lower part of the posterior scalp (mastoid) and shoulder, which occupy an unique area in the homunculus. We analyzed the location of the equivalent current dipole (ECD) of SEF following electrical stimulation of the skin at the face, mastoid and shoulder in 20 normal subjects. Three deflections (1M, 2M and 3M) were obtained within 50 ms of the stimulation in 16 of 20 subjects. The peak latency of the 1M and 2M was not significantly different at any stimulus sites. The amplitude of the 1M was significantly larger following the face than mastoid stimulation (p < 0.05). The 16 subjects were classified according to the locations of the ECD on stimulation of the mastoid: close to that for shoulder stimulation, but significantly (p < 0.05) more superior and medial to that following the face stimulation (Type 1, eleven subjects); close to that for face stimulation, but significantly (P < 0.05) more inferior and lateral to that following the shoulder stimulation (Type 2, five subjects). The site of the receptive area for the posterior scalp shows interindividual variation, possibly due to anatomical differences. [ABSTRACT FROM AUTHOR]