The study has been temporarily suspended due to a low recruitment rate and funding restrictions. Additional funding support is actively being pursued.

We aim to determine if targeted high-definition transcranial direct current stimulation (HD-tDCS) can safely correct errors in visual verticality perception in patients after stroke affecting either hemisphere.

This study explores a new approach to treat graviceptive neglect, a condition that affects balance and perception of uprightness, using a non-invasive brain stimulation technique called HD-tDCS (high-definition transcranial direct current stimulation). Using a phase I/II randomized sham-controlled double-blind parallel clinical trial design, we aim to analyze if HD-tDCS can safely help correct abnormal visual verticality perception in 28 people after stroke. We will also investigate the effects of our protocol on cerebrovascular response using transcranial Doppler and cortical activity using EEG. Neuroanatomical characteristics will be analyzed to establish the relationship between verticality perception error and the extent of temporo-parietal junction (TPJ) damage and, more broadly, the putative VV structural brain Network (VVN). Each participant will receive six HD-tDCS sessions of 2mA for 20 minutes in a central cathode montage applied over the contralesional TPJ. Patients will be randomized into two groups, with 50% receiving active stimulation and 50% receiving sham stimulation. The sham stimulation condition will consist of the same electrode placement, with a 2mA ramp-up over 30 seconds, followed by a 30-second ramp-down. Both groups will undergo 6 sessions, three times a day, for 2 days. The follow-up assessment will be performed 1 month after stimulation.

Inclusion Criteria:

• Supratentorial ischemic stroke diagnosed by neuroimaging and clinical analysis;
• Clinically stable (stable vital signs for 24 hours; no chest pain in the last 24 hours; no significant arrhythmia; no evidence of deep vein thrombosis);
• Normal or corrected-to-normal vision;
• No previous experience with HD-tDCS;
• Ability to provide informed consent (patient or legal representative);
• Ability to comply with the intervention and assessment schedule of the protocol.
• Presence of visual verticality misperception.

Exclusion Criteria:

• Migraine;
• Pregnancy;
• Pacemakers;
• Seizures;
• Claustrophobia;
• Transient ischemic attack;
• Other neurological disorders;
• Psychiatric disorders;
• Sensitive scalp or prior brain surgery;
• Diagnosis of severe carotid atherosclerotic disease (stenosis ≥ 70%);
• Presence of metal implants, cardiac pacemakers, or claustrophobia;
• Diagnosis of COVID-19 or other infectious disease that requires isolation;
• Uncontrolled medical problems, such as terminal cancer or kidney disease.
• Left-handed or mixed-handed individuals as determined using the Edinburgh Handedness Inventory (Appendix 10);
• Peripheral vestibular deficits observed using neuro-otological screening tests when the participant's clinical condition allows (head shake test, head thrust test, Dix-Hallpike, and Pagnini-McClure);
• Prior musculoskeletal disorders affecting alignment and postural balance (e.g., moderate to severe scoliosis; torticollis);
• Cognitive dysfunction outside normal limits on the Mini-Mental State Examination (score below 23);
• Global or Wernicke's aphasia;

Statistician