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.

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.