Stroke is one of the leading causes of serious long-term impairment. According to the estimates, 12,500 people suffer a new or recurrent ischemic stroke in Chile annually, which shows the magnitude of the problem. Motor impairment of the upper limb (UL) stands out as the principal sequel after a CVA (50% of the patients experience it), and the Constraint-Induced Movement Therapy (CIMT) is the rehabilitation approach that shows more scientific evidence today. Even though patients reach certain recuperation levels through this approach, results are still insufficient since 50-80% of the patients continue having upper limb motor impairment after completing standard rehabilitation. Because of this, it is pertinent to conduct research to explore new rehabilitation strategies to reduce the impairment indexes and to provide information for decision making based on evidence.

Recent studies on functional neuroimaging propose that there is an abnormal balance in the motor cortex excitability after stroke - relative under-excitability in the affected hemisphere and over-excitability in the unaffected hemisphere (with the consequent inhibitory influence on ipsilesional regions) in stroke patient with moderate motor impairment. This imbalance in the hemispheres function would limit the possibilities of a greater recovery. Then, in order to reestablish brain balance, the investigators proposed that the early introduction of noninvasive techniques of brain stimulation, such as tDCS, to the motor rehabilitation training could promote improvement of upper limb function in patients with stroke. However, we lack studies that confirm the benefits of using these techniques, define the most appropriate protocols, and determine what patients and under which evolving stages would be the best candidates for treatment.

This study aims to "compare the effectiveness of seven days of bi-hemispheric tDCS, both active and sham, combined with modified CIMT (mCIMT) in the motor and functional recovery of the hemiparetic upper limb in hospitalized patients with subacute unihemispheric stroke at Hospital Clínico de la Universidad de Chile and Hospital San José". This comparison responds to the hypothesis that patients who receive bi-hemispheric and active tDCS combined with mCIMT (experimental group) get at least 30% more recovery of the paretic upper limb compared to the control group who receive sham bi-hemispheric tDCS plus mCIMT after a protocol of seven days treatment.

To test this hypothesis, the investigators propose to carry out a sham randomized multicenter double blind clinical trial. This trial considers seven continuous days of treatment when the participants with hemiparesis as a result of a stroke will be assigned to one of the treatment groups: bi-hemispheric tDCS combined with mCIMT or bi-hemispheric sham tDCS combined with mCIMT. Besides collecting demographic and clinical info from the subjects, the investigators will assess the patients using upper limb scales of functional motor recovery and an evaluation of their functional independence in basic activities of daily living (ADLs). STATA 14.0 software will be used for data analysis.

To date, no study has tested the efficacy of early bi-hemispheric stimulation in combination with mCIMT in subacute hospitalized stroke patients.

Inclusion Criteria:

• First unihemispheric stroke event, ischemic or hemorrhagic, cortical or subcortical.
• Hemiparesis with unilateral brachial compromise.
• Evolution time ≥ 2 days. (equal or more than 2 days after onset)
• Patient must be 18 years old or older.
• Showing ability to perform some movement with the upper limb: at least 20º active extension of the wrist and 10º extension in fingers and/or 20° abduction angle in the shoulder.
• Informed consent signed by the patient.

Exclusion Criteria:

• Previous central injury with motor sequelae.
• Severe aphasia with a score ≥ 2 in the language item of the National Institutes of Health Stroke Scale assessment.
• Severe cognitive impairment with a score < 15 points in the Mini-mental state examination.
• Shoulder subluxation and/or pain > 4 points in the Visual Numeric Scale for pain.
• Non-controlled epilepsy or epileptic seizures in the last three months.
• Metal implants or pacemaker.
• Pregnancy.
• Any other condition that, in the responsible physician's opinion, could prevent the correct development of the treatment.

Still not decided.

Patients will be assigned to the active tDCS plus mCIMT group or to the sham tDCS plus mCIMT group using randomized blocking to ensure the balance between the treatments. Once the person in charge of recruiting receives the patient's informed consent, he will notify this to the person in charge of randomization who will not have any relationship with the patient, will not know the patient's clinical record, and will not be influenced by the head researchers, the evaluators, or the therapist. This person will send a text message to the person responsible for programming and installing the tDCS, who will proceed to set the tDCS either active or simulated. Patients, treating occupational therapists, and the results evaluator will be kept masked to the assignment process.