Doug Bonderud

May 19th 2021

Sequential Brain Stimulation: Shaping the Future of Supplemental Sight


Could a brain bypass help to bring back the sense of sight? Noninvasive electrical brain stimulation may have this potential. As new research published in Cell demonstrates, cutting out the cortical middleman of damaged eyes or optic nerves and going directly to the visual cortex itself makes it possible for both blind and sighted participants to “see” shapes traced directly onto their brains using sequenced electrode activation.

The approach offers prescriptive promise for restoring vision. Improved technology makes it possible to activate more neurons in sequence — while simultaneously increasing the specificity of stimulation at scale. Here’s a quick look at this evolving electric approach.

What You See Is What You Get

A review in Clinical Neurophysiology explains that “the visual system has one of the most complex structures of all sensory systems and is perhaps the most important sense for everyday life.” While our five senses working in tandem help to provide a more nuanced environmental experience, modern human existence relies on sight significantly more than the other four senses. For example, while our sense of taste is instrumental in identifying potentially poisonous provisions, sight offers a shortcut to spot these food-related risks before they reach our mouths.

But what happens when our perceptive pathways don’t work properly? According to an analysis published in Progress in Brain Research, retinal or cerebral visual injury (CVI) was long thought to be irreversible, leaving those affected with no way to regain their sense of sight. However, evolving research efforts have found that, in most cases, the damage caused is not complete. In some cases, only partial damage exists at the visual field border. In others, there may be “islands” of surviving tissue — extrastriate pathways that have escaped unharmed or high-level neuronal networks that are not impacted.

This partially functional paradigm could be the starting point for sight restoration using brain stimulation. If existing, undamaged structures could be either reactivated or taught to perform additional functions previously handled by other pathways, visual operations could be restored.

Shaping the Future of Sight

While electrical brain stimulation to restore partial sight has been on the research radar for decades, the approach has been largely unsuccessful. According to Science magazine, part of the problem stemmed from over stimulation, because electrodes placed on the surface of the brain required substantial current volumes and, therefore, limited the number of nodes that could be activated in tandem without causing potential harm.

However, recent work from the Baylor College of Medicine in Houston took a different approach. By using implanted electrodes stimulated in dynamic sequences, the Baylor team was able to “trace” shapes on participants’ visual cortices, which they were then able to see and identify, according to a press release published in Science Daily.

Interested in the applicability of their approach for both blind and sighted individuals, the Baylor study tested their framework on four sighted patients using implanted electrodes used to monitor epilepsy, as well as two blind participants using electrodes implanted over their visual cortex. In both cases, the strategy was the same: sequential stimulation of multiple electrodes to trace the shape of specific letters. Each test group reported the same results — using sequential brain stimulation, they were able to see and identify the letters produced. It makes sense, since our brains work in similar fashion to search engines, finding familiar frameworks that align with information gleaned from sensory input. By offering an easy-to-follow trace technique, participants were able to connect the contextual dots.

Pinpointing Potential Problems

Efforts at restoring vision have historically encountered the pinpoint problem. By treating each individual electrode like a pixel in a larger image and activating them simultaneously, many participants found that they were able to perceive specific points of light but not the overall image. The Baylor approach sidesteps this issue with sequential, shape-based stimulation, but Michael Beauchamp, the first author of the study, notes that challenges remain on the road to practical, clinical use. The first of these is complexity.

“The primary visual cortex, where the electrodes were implanted, contains half a billion neurons,” he says in the Science Daily press release. “In this study, we stimulated only a small fraction of these neurons with a handful of electrodes. An important next step will be to work with neuroengineers to develop electrode arrays with thousands of electrodes to stimulate more precisely.” Beauchamp also points to the need for improved algorithms capable of delivering enhanced sequential stimulation to “help realize the dream of delivering useful visual information to blind people.”

There’s also a case to be made for multiple methodologies in the effort to improve visual function. For example, an eye-training system designed by Professor of Ophthalmology Krystel Huxlin at the University of Rochester has been shown to help recovering stroke patients regain some of their previously lost sight by teaching undamaged portions of the neural system to processes different types of visual information. Combined with transcranial random noise stimulation (tRNS), the approach offered significant benefits for vision recovery. Extended further to align with sequential stimulation developments, this multi-modal approach could help patients not only recognize specific shapes but rearchitect critical brain connections and effectively bypass the damaged portions of their visual cortex.

Sight remains a complex — and critical — part of the human sensory experience. And while full restoration isn’t yet possible, sequential brain stimulation is helping to shape the future of supplemental sight.