20 Hz tACS engages striatal THINs to enhance β-band synchrony and motor drive.

BACKGROUND: Transcranial alternating current stimulation (tACS) is a noninvasive neuromodulation technique that can enhance motor function. The striatum is a central hub for motor control and β-band oscillations, and its tyrosine hydroxylase-positive interneurons (THINs) are modulated by dopamine. However, whether THINs are associated with motor changes following tACS through β-band synchrony has not been investigated. METHODS: Eighteen-month-old male mice received 20 Hz tACS or sham stimulation over M1 for 7 days under sevoflurane anesthesia. Motor performance, EEG, striatal dopamine release, and THIN activation were assessed at 3 min after awakening on day 7. THINs were optogenetically manipulated during the reaching task under the same post-anesthesia testing window. RESULTS: Transcranial alternating current stimulation was associated with higher post-anesthesia reaching success, increased β-band power, elevated dopamine release, and enhanced THIN activation compared to sham. Optogenetic THIN activation recapitulated motor improvement and β-band enhancement. Optogenetic THIN inhibition reduced successful attempts per minute and β-band power, but no statistically significant reduction in success rate was detected. CONCLUSION: These findings suggest that 20 Hz tACS over M1 may improve post-anesthesia motor performance in aged mice, with converging evidence implicating striatal dopamine release, THIN engagement, and β-band synchrony as functionally coupled elements in the context of post-anesthesia motor recovery in aged mice.