Repetitive Transcranial Magnetic Stimulation of the Primary Somatosensory Cortex Modulates Perception of the Tendon Vibration Illusion

Modulation of somatosensation by transcranial magnetic stimulation over somatosensory cortex: a systematic review

Over the last three decades, transcranial magnetic stimulation (TMS) has gained popularity as a tool to modulate human somatosensation. However, the effects of different stimulation types on the multiple distinct subdomains of somatosensation (e.g., tactile perception, proprioception and pain) have not been systematically compared. This is especially notable in the case of newer theta-burst stimulation protocols now in widespread use. Here, we aimed to systematically and critically review the existing TMS literature and provide a complete picture of current knowledge regarding the role of TMS in modulating human somatosensation across stimulation protocols and somatosensory domains. Following the PRISMA guidelines, fifty-four studies were included in the current review and were compared based on their methodologies and results. Overall, findings from these studies provide evidence that different types of somatosensation can be both disrupted and enhanced by targeted stimulation of specific somatosensory areas. Some mixed results, however, were reported in the literature. We discussed possible reasons for these mixed results, methodological limitations of existing investigations, and potential avenues for future research.

Therapeutic benefits of noninvasive somatosensory cortex stimulation on cortical plasticity and somatosensory function: a systematic review

Optimal limb coordination requires efficient transmission of somatosensory information to the sensorimotor cortex. The primary somatosensory cortex (S1) is frequently damaged by stroke, resulting in both somatosensory and motor impairments. Noninvasive brain stimulation (NIBS) to the primary motor cortex is thought to induce neural plasticity that facilitates neurorehabilitation. Several studies have also examined if NIBS to the S1 can enhance somatosensory processing as assessed by somatosensory-evoked potentials (SEPs) and improve behavioral task performance, but it remains uncertain if NIBS can reliably modulate S1 plasticity or even whether SEPs can reflect this plasticity. This systematic review revealed that NIBS has relatively minor effects on SEPs or somatosensory task performance, but larger early SEP changes after NIBS can still predict improved performance. Similarly, decreased paired-pulse inhibition in S1 post-NIBS is associated with improved somatosensory performance. However, several studies still debate the role of inhibitory function in somatosensory performance after NIBS in terms of the direction of the change (that, disinhibition or inhibition). Altogether, early SEP and paired-pulse inhibition (particularly inter-stimulus intervals of 30-100 ms) may become useful biomarkers for somatosensory deficits, but improved NIBS protocols are required for therapeutic applications.

Effect of repetitive transcranial magnetic stimulation on altered perception of One's own face

BACKGROUND

Chronic orofacial pain (COP) patients often perceive the painful face area as "swollen" without clinical signs; such self-reported illusions of the face are termed perceptual distortion (PD). The pathophysiological mechanisms underlying PD remain elusive.

OBJECTIVE

To test the neuromodulatory effect of repetitive transcranial magnetic stimulation (rTMS) on PD in healthy individuals, to gain insight into the cortical mechanisms underlying PD.

METHODS

PD was induced experimentally by injections of local anesthetic (LA) around the infraorbital nerve and measured as perceived size changes of the affected area. Participants were randomly allocated to inhibitory rTMS (n = 26) or sham rTMS (n = 26) group. The participants rated PD at baseline, 6 min after LA, immediately, 20 and 40 min after rTMS. The rTMS (inhibitory and sham) was applied to face (lip) representation area of primary somatosensory cortex (SI) as an intervention at 10 min after the LA, when the magnitude of PD is large. As inhibitory rTMS, continuous theta-burst stimulation paradigm (50 Hz) for 40s was employed to inhibit cortical activity.

RESULTS

We demonstrated a significant decrease in the magnitude of PD immediately and 20 min after the application of inhibitory rTMS compared with sham rTMS (P < 0.006). In two control experiments, we also showed that peripheral muscle stimulation and stimulation of a cortical region other than the lip representation area had no effect on the magnitude of the PD.

CONCLUSIONS

Inhibitory rTMS applied to a somatotopical-relevant cortical region modulates PD of the face in healthy individuals and could potentially have therapeutic implications for COP patients.

The association between brain activity and motor imagery during motor illusion induction by vibratory stimulation

Background:

The association between motor imagery ability and brain neural activity that leads to the manifestation of a motor illusion remains unclear.

Objective:

In this study, we examined the association between the ability to generate motor imagery and brain neural activity leading to the induction of a motor illusion by vibratory stimulation.

Methods:

The sample consisted of 20 healthy individuals who did not have movement or sensory disorders. We measured the time between the starting and ending points of a motor illusion (the time to illusion induction, TII) and performed electroencephalography (EEG). We conducted a temporo-spatial analysis on brain activity leading to the induction of motor illusions using the EEG microstate segmentation method. Additionally, we assessed the ability to generate motor imagery using the Japanese version of the Movement Imagery Questionnaire-Revised (JMIQ-R) prior to performing the task and examined the associations among brain neural activity levels as identified by microstate segmentation method, TII, and the JMIQ-R scores.

Results:

The results showed four typical microstates during TII and significantly higher neural activity in the ventrolateral prefrontal cortex, primary sensorimotor area, supplementary motor area (SMA), and inferior parietal lobule (IPL). Moreover, there were significant negative correlations between the neural activity of the primary motor cortex (MI), SMA, IPL, and TII, and a significant positive correlation between the neural activity of the SMA and the JMIQ-R scores.

Conclusion:

These findings suggest the possibility that a neural network primarily comprised of the neural activity of SMA and M1, which are involved in generating motor imagery, may be the neural basis for inducing motor illusions. This may aid in creating a new approach to neurorehabilitation that enables a more robust reorganization of the neural base for patients with brain dysfunction with a motor function disorder.

Benefits of using transcranial magnetic stimulation as a tool to facilitate the chronic knee injury rehabilitation

[Purpose] While primary motor cortex activation has been implicated as a key factor in the arthrogenic muscle inhibition after knee joint injury, no viable rehabilitation protocol has been developed to accommodate this factor. In this study, transcranial magnetic stimulation was applied as a means of dissipating arthrogenic muscle inhibition by introducing temporary motor cortex excitation prior to the rehabilitation. [Subjects and Methods] Twenty-four subjects who have underwent the surgery due to knee injury were recruited, and randomly assigned to the control or the simulation groups. The levels of electromyography signals during the maximum voluntary contraction of the quadriceps muscle before, during, and after training designed for the quadriceps strength rehabilitation were measured. [Results] When compared to controls, subjects who received the transcranial magnetic stimulations showed significantly increased levels of voluntary muscle contraction after the training. Moreover, the beneficial effect of the stimulation increased as the rehabilitation progressed. [Conclusion] Transcranial magnetic stimulation itself does not directly improve the symptoms related to knee injuries. However, the use of this technique can provide a time window for effective intervention by dissipating the unwanted effect of the arthrogenic muscle inhibition during rehabilitation.