Priming Theta Burst Stimulation for Stroke: A Study of Intensity

Objectives: To compare the effects of low intensity priming intermittent theta burst stimulation (iTBS) with those derived from conventional intensity priming iTBS, nonpriming iTBS, and sham stimulation in terms of improving hemiparetic upper limb motor functionality and modulating cortical excitation/inhibition in patients with stroke.

Hypothesis to be tested: We hypothesize that low intensity priming iTBS can maximize the induction of therapeutically beneficial metaplasticity, and that this will be reflected in enhanced cortical excitation and reduced cortical inhibition, thereby enabling superior upper limb motor recovery in patients with stroke.

Design and subjects: A randomized controlled trial involving 108 patients with chronic stroke.

Study instruments: Transcranial magnetic stimulation (TMS) and electroencephalography (EEG).

Interventions: Participants will be randomly assigned into one of the following four groups: (1) low intensity priming iTBS (55% resting motor threshold [RMT] continuous theta burst stimulation [cTBS]+70% RMT iTBS); (2) conventional intensity priming iTBS (70% RMT cTBS+70% RMT iTBS); (3) nonpriming iTBS (sham cTBS+70% RMT iTBS); and (4) sham stimulation (sham cTBS+sham iTBS). All participants will receive 60-minute standard motor training after completion of the stimulation program. The intervention will last four weeks, with three sessions per week.

Main outcome measures: Upper limb motor tests and levels of cortical excitation/inhibition measured by TMS-evoked EEG potentials.

Data analysis: Analysis of variance (ANOVA). Expected results: The low intensity priming iTBS protocol will be the most efficacious protocol for enhancing cortical excitation and reducing cortical inhibition in post-stroke patients and will thereby produce superior outcomes with regard to upper limb motor functionality.

Inclusion criteria

• Unilateral upper limb motor dysfunction caused by ischemic stroke, with stroke onset≥6 months. Diagnosis will be verified using discharge summary and radiological reports issued by Hospital Authority. Qualifying participants will undergo structural magnetic resonance imaging (MRI) at the University Research Facility in Behavioral and Systems Neuroscience (UBSN) at PolyU to further confirm their lesion location in the period of experimental participation.
• Age between 18 and 80 years.
• Residual upper limb functions between levels 2-6 in the FTHUE, indicating moderately-to-severely impaired upper limb motor functions.
• Capable of providing informed written consent. Exclusion Criteria

Patients who meet any of the following criteria will be excluded:

• any contraindications to TMS (screened by the safety checklist by Rossi(33)) and/or MRI (screened by the MRI safety checklist offered by UBSN [see supplement]).
• Diagnosed with any concomitant neurological disease other than stroke.
• signs of cognitive impairment, with a Montreal cognitive assessment score<21/22 out of 30 (34).
• Severe spasticity in the hemiparetic upper limb muscles, with a Modified Ashworth score > 2 (35).