ABSTRACT NUMBER: ESOC2026YS72 OPTIMIZING THE INTENSITY OF PRIMING THETA BURST MAGNETIC STIMULATION TO IMPROVE HEMIPARETIC UPPER LIMB MOTOR FUNCTIONS AFTER ISCHEMIC STROKE (THE PRIME-STROKE TRIAL)

Abstract Background and aims Intermittent theta burst stimulation (iTBS) is a promising for poststroke rehabilitation. To stabilize this variability and enhance the clinical benefits of iTBS, we have proposed a novel metaplasticity-elicited priming paradigm involving an inhibitory session using continuous theta burst stimulation (cTBS) followed by an excitatory iTBS session (priming iTBS; Zhang et al., 2022, Stroke). While preceding cTBS at 70% RMT can lower the threshold for LTP induction, it may also suppress overall corticomotor excitability, potentially counteracting the subsequent iTBS (Zhang et al., 2025, Brain Stimulation). Here we aim to determine whether a low-intensity priming iTBS to the ipsilesional motor cortex produces superior improvements in upper-extremity recovery and cortical excitability compared to other protocols in ischemic stroke patients. Methods Participants are randomized to one of four 4-week interventions: low-intensity priming (55% RMT cTBS+iTBS); conventional priming (70% RMT cTBS+iTBS); nonpriming (sham cTBS+iTBS); and sham. All receive 60-minute motor training post-stimulation. The primary outcome is the change in the Fugl-Meyer-Assessment–Upper Extremity (FMA-UE). Secondary outcomes include transcranial-magnetic-stimulation-evoked potentials in concurrent TMS-EEG and upper-extremity functional measures. Results Of 124 planned participants, 24 have completed the intervention. Preliminary FMA-UE analysis finds that the low-intensity priming iTBS improves the most numerically, and all active stimulation show greater gains than the sham stimulation - a trend that is consistent across other functional measures of the upper-extremity. Neurophysiological data will be presented at the conference. This trial is the first to investigate the impact of intensity within a metaplasticity-induced priming protocol for poststroke rehabilitation. Conflict of interest None