Interhemispheric Inhibition Induced by Transcranial Magnetic Stimulation Over Primary Sensory Cortex

The present study investigated whether the long-interval interhemispheric inhibition (LIHI) is induced by the transcranial magnetic stimulation over the primary sensory area (S1-TMS) without activation of the conditioning side of the primary motor area (M1) contributing to the contralateral motor evoked potential (MEP), whether the S1-TMS-induced LIHI is dependent on the status of the S1 modulated by the tactile input, and whether the pathways mediating the LIHI are different from those mediating the M1-TMS-induced LIHI. In order to give the TMS over the S1 without eliciting the MEP, the intensity of the S1-TMS was adjusted to be the sub-motor-threshold level and the trials with the MEP response elicited by the S1-TMS were discarded online. The LIHI was induced by the S1-TMS given 40 ms before the test TMS in the participants with the attenuation of the tactile perception of the digit stimulation (TPDS) induced by the S1-TMS, indicating that the LIHI is induced by the S1-TMS without activation of the conditioning side of the M1 contributing to the contralateral MEP in the participants in which the pathways mediating the TPDS is sensitive to the S1-TMS. The S1-TMS-induced LIHI was positively correlated with the attenuation of the TPDS induced by the S1-TMS, indicating that the S1-TMS-induced LIHI is dependent on the effect of the S1-TMS on the pathways mediating the TPDS at the S1. In another experiment, the effect of the digit stimulation given before the conditioning TMS on the S1- or M1-TMS-induced LIHI was examined. The digit stimulation produces tactile input to the S1 causing change in the status of the S1. The S1-TMS-induced LIHI was enhanced when the S1-TMS was given in the period in which the tactile afferent volley produced by the digit stimulation just arrived at the S1, while the LIHI induced by above-motor-threshold TMS over the contralateral M1 was not enhanced by the tactile input. Thus, the S1-TMS-induced LIHI is dependent on the status of the S1 modulated by the tactile input, and the pathways mediating the sub-motor-threshold S1-TMS-induced LIHI are not the same as the pathways mediating the above-motor-threshold M1-TMS-induced LIHI.

Changes in sensorimotor regions of the cerebral cortex in congenital amusia: a case-control study

Perceiving pitch is a central function of the human auditory system; congenital amusia is a disorder of pitch perception. The underlying neural mechanisms of congenital amusia have been actively discussed. However, little attention has been paid to the changes in the motor rain within congenital amusia. In this case-control study, 17 participants with congenital amusia and 14 healthy controls underwent functional magnetic resonance imaging while resting with their eyes closed. A voxel-based degree centrality method was used to identify abnormal functional network centrality by comparing degree centrality values between the congenital amusia group and the healthy control group. We found decreased degree centrality values in the right primary sensorimotor areas in participants with congenital amusia relative to controls, indicating potentially decreased centrality of the corresponding brain regions in the auditory-sensory motor feedback network. We found a significant positive correlation between the degree centrality values and the Montreal Battery of Evaluation of Amusia scores. In conclusion, our study identified novel, hitherto undiscussed candidate brain regions that may partly contribute to or be modulated by congenital amusia. Our evidence supports the view that sensorimotor coupling plays an important role in memory and musical discrimination. The study was approved by the Ethics Committee of the Second Xiangya Hospital, Central South University, China (No. WDX20180101GZ01) on February 9, 2019.