Suddenly you can’t see to one side.
It’s not that your left eye (or right) has stopped working entirely. It’s that you lose half of the visual field in both eyes. It’s like wearing glasses with a half-blinder on both lenses.
The condition is called homonymous hemianopia (sometimes spelled hemianopsia). Imagine how many everyday activities would be difficult, extremely inconvenient, or even impossible if you couldn’t see to one side. How would hemianopia affect a simple drive or bike-ride? Reading a book? Playing sports? Cooking with multiple hot burners, pans, and pots? Taking care of children or an elderly parent?
Until now, because hemianopia had no cure, patients suffering from the condition simply had to learn how to live with a massively reduced quality of life. Therapy was available, but even months of neurorehabilitative training provided only moderate restoration of vision.
The problem is that the brain coordinates activity across visual regions so it can perform various functions, including detecting motion. When the regions collaborate correctly, they exchange data in perfectly synchronized electrical brain rhythms called oscillations. But a stroke can destroy that synchronicity, leaving people “half-blind.”
But finally there’s hope.
In their Brain paper “Boosting hemianopia recovery: the power of interareal cross-frequency brain stimulation,” lead authors Estelle Raffin, Michele Bevilacqua and colleagues from Switzerland’s École Polytechnique Fédérale de Lausanne (EPFL) revealed that their proof-of-concept, placebo-controlled, double-blind (pardon the expression) clinical trial of a new therapy is showing benefits.
The researchers non-invasively stimulated the brains of 16 patients with stroke-related vision loss, and those patients undertook “two blocks of 10 daily training sessions of a direction discrimination task” whose purpose was “to stimulate the edge of their blind field” while they received with “one of the two cross-frequency transcranial alternative brain stimulation conditions.”
The result? Vastly improved vision even among those who’d suffered from hemianopia for a long time.
Because studies showed that externally stimulating oscillations could restore synchronicity, Friedhelm Hummel, the project’s lead researcher at EPFL's Neuro-X Institute, explains that his team “applied an innovative novel treatment strategy based on orchestrated bifocal non-invasive [electrical] brain stimulation to the visual system.” Its inspiration was the brain’s own, natural physiological functioning.
As an additional victory for the trial, Hummel’s team identified factors “associated with response to the treatment, potential biomarkers for patient stratification,” meaning an efficient medical sorting of patients to identify those with the highest likelihood of success for the EPFL treatment.
In the study, researchers used cross-frequency bifocal transcranial alternating current stimulation (cf-tACS) with one group of patients to synchronize brain oscillations between two brain regions: the medio-temporal area and the primary visual cortex. By stimulating the two areas with different frequencies of electrical signals, they reproduced the brain's own communication pattern.
To be more precise, the scientists applied forward-pattern cf-tACS, which sends high-frequency gamma waves to the motion-sensitive area, and low-frequency alpha waves to the primary visual cortex, an approach just like the brain’s bottom-to-top information flow during visual processing, helping to re-establish disrupted communication after stroke.
Patients receiving forward-pattern cf-tACS displayed far greater improvement in perceiving motion than those who got the reverse-pattern control, and brain scans and electro-encephalography confirmed the restored communication between the medio-temporal area and the primary visual cortex, and the EGG showed improved synchronicity among regions.
While in-laboratory improvements were impressive – some patients “experienced measurable expansions in their visual fields” – real-world results offer even more poignant examples of progress, with one man saying he could at last see his wife’s right arm while she was driving and he was sitting in the passenger seat beside her.
While visual training will likely continue to be a productive part of treatment for people with hemianopia, the EPFL study demonstrates that external brain stimulation with cf-tACS is a promising method for improving vision, and with it, quality of life.
Source: EPFL
