No effects of cerebellar transcranial random noise stimulation on cerebellar brain inhibition, visuomotor learning, and pupil diameter.

Cerebellar brain inhibition (CBI) is an inhibitory output from the cerebellum to the primary motor cortex, which is decreased in early motor learning. Transcranial random noise stimulation (tRNS) is a noninvasive brain stimulation to induce brain plastic changes; however, the effects of cerebellar tRNS on CBI and motor learning have not been investigated yet to our knowledge. In this study, whether cerebellar tRNS decreases CBI and improves motor learning was examined, and pupil diameter was measured to examine physiological changes due to the effect of tRNS on motor learning. Thirty-four healthy subjects were assigned to either the cerebellar tRNS group or the Sham group. The subjects performed visuomotor tracking task with ten trials each in the early and late learning stages while receiving the stimulus intervention. CBI and motor evoked potentials were measured before the learning task, after the early learning stage, and after the late learning stage, and pupil diameter was measured during the task. There was no change in CBI in both groups. No group differences in motor learning rates were observed at any learning stages. Pupil diameter was smaller in the late learning stage than in the early learning stage in both groups. The cerebellar tRNS was suggested not to induce changes in CBI and improvement in motor learning, and it did not affect pupil diameter.

Changes in excitability and GABAergic neuronal activity of the primary somatosensory cortex after motor learning.

Introduction: It is widely known that motor learning changes the excitability of the primary motor cortex. More recently, it has been shown that the primary somatosensory cortex (S1) also plays an important role in motor learning, but the details have not been fully examined. Therefore, we investigated how motor skill training affects somatosensory evoked potential (SEP) in 30 neurologically healthy subjects. Methods: SEP N20/P25_component and N20/P25 SEP paired-pulse depression (SEP-PPD) were assessed before and immediately after complex or simple visuomotor tasks. Results: Motor learning was induced more efficiently by the complex visuomotor task than by the simple visuomotor task. Both the N20/P25 SEP amplitude and N20/P25 SEP-PPD increased significantly immediately after the complex visuomotor task, but not after the simple visuomotor task. Furthermore, the altered N20/P25 SEP amplitude was associated with an increase in motor learning efficiency. Conclusion: These results suggest that motor learning modulated primary somatosensory cortex excitability.

Transcranial direct current stimulation and transcranial random noise stimulation over the cerebellum differentially affect the cerebellum and primary motor cortex pathway.

Transcranial direct current stimulation (tDCS) and transcranial random noise stimulation (tRNS) are two methods of noninvasively modulating cortical excitability below the placed electrode. Anodal tDCS over the cerebellum has been shown to modulate cerebellar brain inhibition (CBI), which is an indication of cerebellar excitability, but does not alter contralateral M1 excitability. However, the effect of tRNS over the cerebellum has not been investigated. The purpose of this study was thus to compare the effects of tDCS and tRNS over the cerebellum on CBI and the contralateral motor evoked potentials (MEPs), as well as on the relationship between CBI and contralateral MEPs. A total of 15 healthy subjects completed four-condition transcranial electrical stimulation (tES) interventions (anodal tDCS_1 mA, anodal tDCS_2 mA, tRNS, and Sham) on separate days. CBI and MEPs were measured using transcranial magnetic stimulation (TMS) before and after the 20 min tES intervention. For all conditions, there were no significant differences before and after tES in CBI or contralateral MEPs. In contrast, following tRNS, changes in CBI and MEPs were significantly correlated. No significant correlations were found in the other three conditions, indicating that cerebellar tDCS and tRNS have distinct effects on the relationship between CBI and contralateral MEPs. Taken together, these findings suggest that cerebellar tRNS may modulate the cerebellar to contralateral M1 pathway.

Influence of Catechol-O-Methyltransferase Gene Polymorphism on the Correlation between Alexithymia and Hypervigilance to Pain.

The psychological characteristic of having difficulty expressing emotions, known as alexithymia, is associated with hypervigilance to pain and is considered one of the risk factors for chronic pain. The correlation between alexithymia and hypervigilance to pain can be observed even in healthy individuals. However, the factors influencing this correlation remain unknown. We explored the dopamine system, which is known to be involved in emotion and pain. The dopamine-degrading enzyme catechol-O-methyltransferase (COMT) has a genetic polymorphism known to influence dopamine metabolism in the prefrontal cortex. COMT polymorphism reportedly affects various aspects of pain and increases pain sensitivity in Met allele carriers. Therefore, we investigated whether the correlation between alexithymia and hypervigilance to pain is influenced by COMT polymorphism in healthy individuals. The results revealed a significant positive correlation between the "difficulty describing feelings" of the 20-item Toronto Alexithymia Scale and the "attention to changes in pain" of the pain vigilance and awareness questionnaire in COMT Met carriers but not in Val/Val individuals. This finding suggests that the correlation between alexithymia and hypervigilance to pain is influenced by COMT polymorphism.