Theta-burst stimulation over primary somatosensory cortex modulates the tactile acuity of the tongue

Emerging studies in humans have established the modulatory effects of repetitive transcranial magnetic stimulation (rTMS) over primary somatosensory cortex (S1) on somatosensory cortex activity and perception. However, to date, research in this area has primarily focused on the hand and fingers, leaving a gap in our understanding of the modulatory effects of rTMS on somatosensory perception of the orofacial system and speech articulators. The present study aimed to examine the effects of different types of theta-burst stimulation (TBS)-continuous TBS (cTBS), intermittent TBS (iTBS), or sham-over the tongue representation of left S1 on tactile acuity of the tongue. In a repeated-measures design, 15 volunteers participated in four separate sessions, where cTBS, iTBS, sham, or no stimulation was applied over the tongue representation of left S1. Effects of TBS were measured on both temporal and spatial perceptual acuity of the tongue using a custom vibrotactile stimulator. Results showed that cTBS significantly impaired spatial amplitude threshold at the time window of 16-30 min after stimulation, whereas iTBS improved it at the same time window. The effect of iTBS, however, was smaller than cTBS. In contrast, neither cTBS nor iTBS had any effect on the temporal discrimination threshold. The current study establishes the validity of using TBS to modulate somatosensory perception of the orofacial system. Directly modifying somatosensation in the orofacial system has the potential to benefit clinical populations with abnormal tactile acuity, improve our understanding of the role of sensory systems in speech production, and enhance speech motor learning and rehabilitation.<b>NEW & NOTEWORTHY</b> The current study examines the effects of different types of theta-burst stimulation (TBS) [continuous TBS (cTBS), intermittent TBS (iTBS), sham] over the tongue representation of left primary somatosensory cortex (S1). Results show that the spatial acuity of the tongue can be impaired or improved by cTBS or iTBS, respectively. Directly modifying somatosensation in the orofacial system can benefit clinical populations with abnormal tactile acuity, advance our understanding of sensory systems in speech production, and improve speech motor learning and rehabilitation.