Reduction in motor error by presenting subthreshold somatosensory information during visuomotor tracking tasks.

Weak sensory noise acts on the nervous system and promotes sensory and motor functions. This phenomenon is called stochastic resonance and is expected to be applied for improving biological functions. This study investigated the effect of electrical stimulation on grip force adjustment ability.

High-resolution EEG source localization in personalized segmentation-free head model with multi-dipole fitting.

. Electroencephalograms (EEGs) are often used to monitor brain activity. Several source localization methods have been proposed to estimate the location of brain activity corresponding to EEG readings.

Selective stimulation of nociceptive small fibers during intraepidermal electrical stimulation: Experiment and computational analysis.

Electrical stimulation of skin nociceptors is gaining attention in pain research and peripheral neuropathy diagnosis. However, the optimal parameters for selective stimulation are still difficult to determine because they require simultaneous characterization of the electrical response of small fibers (Aδ- and C-fibers). In this study, we measured the electrical threshold responses of small fibers to train-pulse stimulation in humans for the first time.

Visuomotor Tracking Task for Enhancing Activity in Motor Areas of Stroke Patients.

Recovery of motor function following stroke requires interventions to enhance ipsilesional cortical activity. To improve finger motor function following stroke, we developed a movement task with visuomotor feedback and measured changes in motor cortex activity by electroencephalography. Stroke patients performed two types of movement task on separate days using the paretic fingers: a visuomotor tracking task requiring the patient to match a target muscle force pattern with ongoing feedback and a simple finger flexion/extension task without feedback.

Dexterous manual movement facilitates information processing in the primary somatosensory cortex: A magnetoencephalographic study.

The interaction between the somatosensory and motor systems is important for control of movement in humans. Cortical activity related to somatosensory response and sensory perception is modulated by the influence of movement executing mechanisms. This phenomenon has been observed as inhibition in the short-latency components of somatosensory evoked potentials and magnetic fields (SEPs/SEFs).

Synaptic Effect of Aδ-Fibers by Pulse-Train Electrical Stimulation.

Electrical stimulation of specific small fibers (Aδ- and C-fibers) is used in basic studies on nociception and neuropathic pain and to diagnose neuropathies. For selective stimulation of small fibers, the optimal stimulation waveform parameters are an important aspect together with the study of electrode design. However, determining an optimal stimulation condition is challenging, as it requires the characterization of the response of the small fibers to electrical stimulation.

Electrical Characterisation of Aδ-Fibres Based on Human Electrostimulation Threshold.

Electrical stimulation of small fibres is gaining attention in the diagnosis of peripheral neuropathies, such as diabetes mellitus, and pain research. However, it is still challenging to characterise the electrical characteristics of axons in small fibres (Aδ and C fibres). In particular, measurement for human Aδ-fibre is difficult due to the presence of myelin and ethical reason.

Facilitation of information processing in the primary somatosensory area in the ball rotation task.

Somatosensory input to the brain is known to be modulated during voluntary movement. It has been demonstrated that the response in the primary somatosensory cortex (SI) is generally gated during simple movement of the corresponding body part. This study investigated sensorimotor integration in the SI during manual movement using a motor task combining movement complexity and object manipulation.

Reappraisal of field dynamics of motor cortex during self-paced finger movements.

Background: The exact origin of neuronal responses in the human sensorimotor cortex subserving the generation of voluntary movements remains unclear, despite the presence of characteristic but robust waveforms in the records of electroencephalography or magnetoencephalography (MEG).

Aims: To clarify this fundamental and important problem, we analyzed MEG in more detail using a multidipole model during pulsatile extension of the index finger, and made some important new findings.

Results: Movement-related cerebral fields (MRCFs) were confirmed over the sensorimotor region contralateral to the movement, consisting of a temporal succession of the first premovement component termed motor field, followed by two or three postmovement components termed movement evoked fields.

The cerebral representation of scratching-induced pleasantness.

Itch is an unpleasant sensation with the desire to scratch. Although it is well known that scratching itchy skin is pleasurable, the cerebral mechanisms underlying this phenomenon are poorly understood. We hypothesized that the reward system is associated with scratching-induced pleasantness.

The effect of unpredicted visual feedback on activation in the secondary somatosensory cortex during movement execution.

Background: A mechanism that monitors the congruence between sensory inputs and motor outputs is necessary to control voluntary movement. The representation of limb position is constantly updated on the basis of somatosensory and visual information and efference copy from motor areas. However, the cortical mechanism underlying detection of limb position using somatosensory and visual information has not been elucidated.

Modulation of somatosensory evoked potentials during force generation and relaxation.

This study investigated the modulation of somatosensory evoked potentials (SEPs) during precisely controlled force generation and force relaxation in a visuomotor tracking task. Subjects were instructed to track a target line with a line that represented their own force generated by grip movement with the right hand as accurately as possible during concurrent electrical stimulation. The target force line moved up continuously from 0 to 20 % of maximal voluntary contraction (MVC) (the force generation phase: FG phase) and moved down from 20 to 0 % of MVC (the force relaxation phase: FR phase) in 7 s at a constant velocity.

Conflict caused by visual feedback modulates activation in somatosensory areas during movement execution.

The role of sensory information in motor control has been studied, but the cortical processing underlying cross-modal relationship between visual and somatosensory information for movement execution remains a matter of debate. Visual estimates of limb positions are congruent with proprioceptive estimates under normal visual conditions, but a mismatch between the watched and felt movement of the hand disrupts motor execution. We investigated whether activation in somatosensory areas was affected by the discordance between the intended and an executed action.

The sequence effect in de novo Parkinson's disease.

Background And Purpose: The sequence effect (SE) in Parkinson's disease (PD) denotes progressive slowness in speed or progressive decrease in amplitude of repetitive movements. It is a well-known feature of bradykinesia and is considered unique in PD. Until now, it was well-documented in advanced PD, but not in drug-naïve PD.

Characteristics of the sequence effect in Parkinson's disease.

The sequence effect (SE) in Parkinson's disease (PD) is progressive slowing of sequential movements. It is a feature of bradykinesia, but is separate from a general slowness without deterioration over time. It is commonly seen in PD, but its physiology is unclear.

The effect of stimulus probability on the somatosensory mismatch field.

We investigated the effect of deviant stimulus probability on the somatosensory magnetic mismatch negativity (MMNm) using an electrical two-point stimulation. First, we determined the discrimination threshold (DT) of the two-point distance. We applied standard stimuli at a distance that subjects felt as one point and deviant stimuli at a distance that subjects definitely felt as two points.

Time-varying cortical activations related to visual-tactile cross-modal links in spatial selective attention.

The neural mechanisms underlying unimodal spatial attention have long been studied, but the cortical processes underlying cross-modal links remain a matter of debate. To reveal the cortical processes underlying the cross-modal links between vision and touch in spatial attention, we recorded magnetoencephalographic (MEG) responses to electrocutaneous stimuli when subjects directed attention to an electrocutaneous or visual stimulus presented randomly in the left or right space. Neural responses recorded around the bilateral sylvian fissures at 85 and 100 ms after the electrocutaneous stimulus were significantly enhanced by spatial attention in both the touch-irrelevant and -relevant modalities.

Changes in somatosensory evoked potentials and Hoffmann reflexes during fast isometric contraction of foot plantarflexor in humans.

In the present study, the extent to which the early component of somatosensory evoked potentials (SEPs) and the Hoffmann (H-) reflex induced by stimulation of the posterior tibial nerve are altered during the ascending and descending phases of fast plantarflexion was investigated. SEPSs and H-reflex of the soleus following tibial nerve stimulation were examined during fast plantarfiexion when performed by nine normal subjects. The analyses focused on differences in amplitude modulation of the P30-P40 component of SEP and the H-reflex between the ascending and descending phases of full-wave rectified and averaged soleus electromyographic (EMG) activity.

Objective examination for two-point stimulation using a somatosensory oddball paradigm: an MEG study.

Objective: To establish an objective two-point discrimination test using magnetoencephalography (MEG).

Methods: First, we determined the discrimination threshold (DT) of the two-points. In the first experiment, we applied 0.

Pre-movement modulation of tibial nerve SEPs caused by a self-initiated dorsiflexion.

Objective: To investigate the centrifugal effect on somatosensory evoked potentials (SEPs), we recorded the pre-movement modulation of SEPs following stimulation of the tibial nerve caused by a self-initiated dorsiflexion.

Methods: SEPs following stimulation of the right tibial nerve at the popliteal fossa were recorded during self-initiated dorsiflexion of the right ankle every 5-7s. Based on the onset of Bereitschaftspotential and negative slope, the preparatory period before dorsiflexion was divided into four sub-periods (pre-BP, BP1a, BP1b and BP2 sub-period), and SEPs in each sub-period were averaged.

Centrifugal regulation of human cortical responses to a task-relevant somatosensory signal triggering voluntary movement.

Many studies have reported a movement-related modulation of response in the primary and secondary somatosensory cortices (SI and SII) to a task-irrelevant stimulation in primates. In the present study, magnetoencephalography (MEG) was used to examine the top-down centrifugal regulation of neural responses in the human SI and SII to a task-relevant somatosensory signal triggering a voluntary movement. Nine healthy adults participated in the study.

Active attention modulates passive attention-related neural responses to sudden somatosensory input against a silent background.

To reveal whether active attention modulates neuronal responses related to passive attention to somatosensory stimuli presented suddenly against a silent background, we examined the passive attention-related change in amplitude of the event-related brain potentials (ERPs), caused by temporal infrequency of stimuli. Eighteen healthy subjects performed passive and active attention tasks in two stimulus conditions. In the oddball condition, frequent (80%, standard) and infrequent (20%, deviant) electrical stimuli were randomly delivered to the second and third digits of the left hand.

Higher anticipated force required a stronger inhibitory process in go/nogo tasks.

Objective: We investigated the effect of the inhibitory process with increasing muscle force on event-related potentials (ERPs) and motor evoked potentials (MEPs).

Methods: The subjects performed a S1-S2 paradigm with go/nogo tasks. S1 was an auditory tone burst, and S2 was an electrical stimulation applied to the second (go stimuli) or fifth digit (nogo stimuli) of the left hand.

Centrifugal regulation of a task-relevant somatosensory signal triggering voluntary movement without a preceding warning signal.

A warning signal followed by an imperative signal generates anticipatory and preparatory activities, which regulate sensory evoked neuronal activities through a top-down centrifugal mechanism. The present study investigated the centrifugal regulation of neuronal responses evoked by a task-relevant somatosensory signal, which triggers a voluntary movement without a warning signal. Eleven healthy adults participated in this study.

The characteristics of the nogo-N140 component in somatosensory go/nogo tasks.

Nogo-related brain potentials may not be dependent on sensory modalities but reflect common neural activities specific to the inhibitory process. Recent studies reported that nogo potentials were elicited by not only visual and auditory but also somatosensory stimulation. However, the characteristics of this nogo potential evoked by somatosensory stimulation have been unclear because of the small number of reports.