Individualized Beta Frequency Intermittent Theta Burst Stimulation Enhances Corticospinal Plasticity in Healthy...

Intermittent theta burst stimulation (iTBS) can alter cortical excitability by modulating dendritic plasticity and spine density; however, its efficacy exhibits high interindividual variability. Recent findings suggest that noninvasive brain stimulation with individualized beta-band frequency improves cortical plasticity. This study investigated whether iTBS applied at an individualized beta-band frequency could increase specific cortical excitability (ie, L2/3 interneurons and L5 pyramidal neurons), prolonging effects and reducing variability.

In total, 30 healthy individuals participated in two experiments using a randomized, cross-over design with three conditions: individualized beta-band frequency iTBS (individualized iTBS), conventional iTBS, and sham stimulation. Each intervention was applied for 190 seconds over the left primary motor cortex (M1). For individualized iTBS, the standard 50-Hz burst frequency was replaced with each participant's peak beta-band corticomuscular coherence between electroencephalography over the left M1 and electromyography from the right first dorsal interosseous muscle. In experiment 1, we evaluated the immediate effects of each intervention on motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation in posterior-anterior (PA) and lateral-medial (LM) orientations. In experiment 2, we assessed the duration of changes in corticospinal excitability at 10-minute intervals up to 60 minutes after stimulation.

Individualized iTBS immediately increased PA-MEPs and LM-MEPs, and sustained improvement of corticospinal excitability for up to 50 minutes. Conversely, conventional iTBS induced an immediate increase only in PA-MEPs but failed to produce sustained improvement. Sham iTBS induced no significant changes in either PA-MEPs or LM-MEPs and did not elicit any lasting effects. Furthermore, in experiment 2, responders were defined as individuals with a Post0-to-Pre-MEP ratio >1.15, and the responder rate was higher with individualized iTBS (62.5%) than with conventional iTBS (37.5%).

These findings suggest that individualized beta-band frequency iTBS improves the duration of corticospinal excitability and reduces interindividual variability, possibly through improved specific cortical excitability.