Bifocal Beta-frequency Transcranial Alternating Current Stimulation Enhances Somatosensory Spatial Discrimination

Somatosensory inputs are sequentially processed across multiple brain regions via cortico-cortical networks. Our recent magnetoencephalography (MEG) study identified specific beta-frequency cortico-cortical networks involved in tactile two-point discrimination (TPD), including those between primary somatosensory cortex (S1) and superior parietal lobule (SPL), and between S1 and angular gyrus (AG). These findings prompted us to investigate whether modifying these networks could influence TPD. We therefore examined the effects of bifocal beta-frequency transcranial alternating current stimulation (tACS) on TPD by specifically targeting the relevant networks. Thirty healthy adults participated in the study, which consisted of five sessions: an MRI scan, MEG recording, and three tACS sessions. Resting-state MEG and somatosensory-evoked magnetic fields were acquired using a 306-channel MEG system. During the intervention, 20-min tACS at each participant’s individual frequency was delivered to personalized targets—either the S1–SPL or S1–AG network—or administered as sham. TPD was automatically assessed at ten distances (0–5.0 mm) before, during, and after tACS. Bifocal beta-frequency tACS selectively modulated TPD thresholds at specific distances under both active conditions. Significant improvements were observed when tACS was applied to the S1–SPL network (3.0, 3.5, and 5.0 mm; all P < 0.049) and the S1–AG network (3.5 mm; all P < 0.046), whereas sham condition produced no significant effects. Electric field modeling confirmed that stimulation selectively targeted either the SPL or the AG, depending on the condition (all P < 0.02). Bifocal beta-frequency tACS targeting the S1–SPL or S1–AG network improves TPD.