Rationale: Acute stroke leaves many patients with functional deficits, of which upper extremity motor impairment is one of the most disabling. Evidence from imaging and electrophysiological studies converge on the idea that impaired motor function after stroke is associated with disrupted network activity in the brain. Non-invasive brain stimulation methods, like transcranial magnetic stimulation (TMS), can be used to restore disrupted network activity and have been shown to successfully facilitate recovery of motor function in patients with stroke. Application of continuous theta burst stimulation (cTBS), an inhibitory form of TMS, to the contralesional motor cortex has been shown to improve the recovery of motor function in patients with stroke. However, responsiveness to this treatment varies considerably between stroke patients and the mechanisms through which contralesional cTBS facilitates recovery of motor function remain unclear.

Objective: To determine if contralesional cTBS normalizes interhemispheric inhibition from the contralesional to ipsilesional primary motor cortex stroke patients with motor impairments. Age-matched healthy persons will serve as controls.

Study design: A prospective, open-label within-subject intervention study

Study population: 40 patients with first-ever ischemic stroke in one hemisphere and a unilateral paresis of the upper extremity, and 40 age-matched controls.

Main endpoints: Primary endpoint: Interhemispheric inhibition from the contralesional to ipsilesional primary motor cortex. Secondary endpoints: contralesional intracortical inhibition; effect of contralesional TMS interference on finger tapping frequency.

Inclusion Criteria for patients:

• Age ≥ 18 years;
• First-ever ischemic stroke or intracerebral hemorrhage in a cerebral hemisphere or the brainstem;
• Unilateral paresis of an upper extremity with a Motricity Index (MI) between 9 and 99
• Inclusion possible between 3 weeks and 6 weeks after stroke onset;
• Signed informed consent.

Inclusion Criteria for healthy controls:

• Age ≥ 18 years;
• Signed informed consent.
• Normal motor function with a minimum Motricity Index (MI) of 99.

Exclusion Criteria:

• Disabling medical conditions (severe heart disease, severe head trauma, severe mental illness);
• Severe deficits in communication, memory or understanding which could impede participation, as determined by the treating physician;
• Contraindications to TMS and/or MRI (ferrous implants, history of epilepsy, drug or alcohol abuse over a period of 6 months prior to the experiment, pregnancy);
• Life expectancy shorter than one year;
• Upper limb paresis prior to stroke onset.