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.

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.

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.