The Use of Dual-coil Transcranial Magnetic Stimulation to Measure and Modulate Poststroke Interhemispheric Inhibition.

Objectives: This project will (1) establish the test-retest reliability of a novel transcranial magnetic stimulation-electroencephalography (TMS-EEG) interhemispheric inhibition (IHI) measure and (2) validate it against the TMS-EMG-based IHI measure (the gold standard). It will also (3) compare effects of dual-coil cortico-cortical paired associative stimulation (ccPAS) protocols with different interstimulus intervals (ISI) on this TMS-EEG-based IHI marker in poststroke patients. Methods: Study 1: IHI will be conducted in 20 stroke patients and 20 healthy counterparts using TMS-EEG and TMS-EMG; furthermore, both measures will be repeated after one week for test-retest reliability. Study 2: A randomized-crossover trial where 20 stroke patients undergo a single-session ccPAS in three separate visits (ISI: 8ms: LTD-like, 12ms: LTP-like, 100ms: sham) to investigate the differential modulatory effects in IHI.

Inclusion criteria

• (1) have a diagnosis of ischemic or hemorrhagic stroke, with time after stroke onset≥6 months. For stroke patients, we will invite participants to receive a structural magnetic resonance imaging (MRI) at the University Research Facility in Behavioral and Systems Neuroscience to verify their actual lesion location; (2) aged between 18 and 80 years old; (3) with residual upper limb functions from 4-7 levels in the Functional Test for the Hemiplegic Upper Extremity (Hong Kong version); (4) have evocable MEP from both M1; (5) able to give informed written consent to participate in the study. (6) able to understand and communicate with Chinese.

Exclusion criteria

(1) any contraindications to TMS (screened by the safety checklist by Rossi); (2) any concomitant neurological disease; (3) any sign of moderate-to-severe cognitive problems, i.e., the abbreviated mental test Hong Kong version<6 out of 10 points [22]; and (4) Modified Ashworth score>2 in hand, wrist or elbow extensor muscle in their hemiparetic upper limbs.

In addition, a group of age-matched, right-hand-dominant healthy adults, without any known neurological and psychiatric diseases, will be enrolled.