Non-Invasive Brain Stimulation Improves Visual Recovery After Stroke

A new study from researchers at EPFL introduces a promising non-invasive brain stimulation technique aimed at restoring visual function in stroke patients with hemianopia. The treatment combines visual training with targeted neuromodulation, offering a novel approach to visual rehabilitation in cases where current therapies fall short.

Hemianopia: A Major Barrier in Post-Stroke Recovery

Each year, thousands of stroke survivors experience hemianopia, a condition that results in the loss of vision in half of the visual field, typically split at the vertical midline. This impairment significantly limits daily activities such as reading, navigating crowds, or driving.

Currently, treatment options for hemianopia primarily focus on compensatory strategies, helping patients adapt to vision loss rather than regaining lost function. Intensive neurorehabilitation may lead to moderate recovery, but typically requires months of training, and full restoration of visual fields remains rare.

The underlying challenge is rooted in the brain's inter-regional communication, particularly between the primary visual cortex (V1) and the medio-temporal area (MT), both of which are involved in detecting and processing motion. After a stroke, the synchronized activity between these regions, governed by precise electrical oscillations, can become disrupted, impairing visual performance.

Targeting Brain Oscillations for Visual Restoration

Building on evidence that external brain stimulation can help restore disrupted brain connectivity, researchers at EPFL’s Neuro-X Institute, led by Prof. Friedhelm Hummel, developed a novel therapy that combines visual training with bifocal, non-invasive brain stimulation. This approach was designed to enhance visual recovery in stroke patients with hemianopia by aligning brain activity patterns in a way that reflects natural visual processing.

The treatment strategy specifically targets the physiological mechanisms underlying visual perception, aiming to restore communication between key brain regions using synchronized, frequency-specific stimulation. In addition to evaluating the treatment’s effects, the research also explored factors associated with positive patient outcomes, which may inform future strategies for individualized therapy.

Clinical Trial Demonstrates Efficacy of cf-tACS in Stroke Patients

In a placebo-controlled, double-blind, proof-of-concept clinical trial, first author Dr. Estelle Raffin and colleagues tested this approach on 16 stroke patients with hemianopia. During treatment, participants engaged in a motion-detection task targeting the blind-edge of their visual field while simultaneously receiving cf-tACS.

The stimulation was applied to both the primary visual cortex (V1) and the medio-temporal area (MT). The key was to deliver signals that mimicked the brain’s natural communication flow, known as a forward-pattern:

       • Alpha-frequency (low) stimulation to V1

       • Gamma-frequency (high) stimulation to MT

This configuration reflects the brain’s typical “bottom-up” visual processing pattern and was designed to re-establish disrupted synchronization caused by stroke.

Measurable Improvements in Visual Function and Real-Life Impact

Patients who received forward-pattern cf-tACS showed significantly greater improvements in motion perception compared to the reverse-pattern control group. Many also demonstrated visual field expansions, particularly in the trained areas.

In addition to clinical metrics, some patients reported real-world improvements. One participant shared that after treatment, he was "able to see the right arm of his wife when seated on the passenger seat, when she is driving," something he could not perceive prior to therapy.

EEG data confirmed improved synchronization between the V1 and MT regions, and functional brain imaging showed increased activity in the motion-sensitive area after stimulation. Notably, the greatest benefits were seen in patients whose neural pathways between V1, and MT were still partially intact, indicating that even limited preservation of these circuits can support meaningful recovery.

A Step Toward Accessible Visual Rehabilitation

The study highlights that combining physiology-based neuromodulation with visual training can significantly enhance visual outcomes in stroke survivors with hemianopia. If validated in larger trials, this method could offer a faster, more accessible, and non-invasive therapeutic option where existing interventions remain limited.

Reference:

Estelle Raffin et al, Boosting hemianopia recovery: the power of interareal cross-frequency brain stimulation, Brain (2025). DOI: 10.1093/brain/awaf252