Restoring sensory functions lost due to nervous system injuries or diseases is one of modern medicine's greatest challenges. An international team of researchers, including the Miguel Hernández University of Elche (UMH), has published in the scientific journal Nature Reviews Bioengineering a comprehensive work redefining the technological and clinical roadmap for returning sight and touch through direct brain stimulation.
Generating light points in a blind person's visual field or touch sensations through direct brain stimulation is already possible. However, converting these artificial perceptions into truly useful information for daily life remains a major challenge for sensory neuroprosthetics. An international research team, with the participation of Professor Eduardo Fernández from the Institute of Bioengineering at the Miguel Hernández University of Elche (UMH), has published a study highlighted on the cover of the scientific journal Nature, analyzing the advances and limitations of cortical prostheses aimed at restoring vision and touch in people with blindness or spinal cord injury.
These cortical sensory prostheses target the two brain regions where visual and tactile information is processed: the primary visual cortex (V1) and the primary somatosensory cortex (S1). Trials conducted on volunteer participants have shown that electrical stimulation of these areas using microelectrodes implanted in the brain can evoke phosphenes—luminous dots or shapes—and localized tactile sensations. However, reproducing complex, stable, and natural perceptions remains difficult due to the brain's complexity and the limitations of electrode stability over time.
The key technology in this field is intracortical stimulation, meaning through microelectrodes implanted within the brain tissue itself, highlights UMH professor Eduardo Fernández. "By coordinating the stimulation of multiple microelectrodes, we not only enable a blind person to distinguish contours or shapes, but it's also possible to move towards restoring the sensation of touch. In both cases, it involves stimulating a part of the brain responsible for processing a specific sensory modality, but the basis and challenges are similar."
The authors propose that the immediate goal does not necessarily have to be to exactly replicate a natural sense. As an example, they recall cochlear implants, which convert sound into electrical signals and directly stimulate the auditory nerve. The information reaching the brain is much simpler than in natural hearing, but the brain learns to interpret it, turning it into a functional experience. "A neuroprosthesis can be functional if it provides artificial information that the brain can learn to interpret and use, for example, to locate objects, navigate, or better control a robotic limb," explains Eduardo Fernández. Their success should also be evaluated by usability, learning capacity, and utility for individuals, while restoring natural sensory perception would be the long-term objective, according to the researchers.
The study identifies 12 research groups worldwide that have conducted human trials with visual or somatosensory cortical prostheses, involving only 35 participants over 58 years. "This figure reflects the extent to which these technologies are still in an experimental phase, and therefore, the available evidence in humans is still limited," points out Fernández Jover. The UMH is part of this small international group, with five trials on volunteers who have been implanted with microelectrode arrays capable of stimulating and recording activity in the visual cortex.
The work emphasizes that the next crucial step for the clinical and commercial transfer of these systems involves developing more stable and flexible interfaces, new stimulation strategies, combining different sensory modalities, and creating systems that can adapt to each user. The researchers also believe it is important to leverage the brain's own capacity to learn to interpret new signals, which will be a key factor for future generations of neuroprostheses.
This study helps lay the clinical foundations for the next generation of sensory neuroprostheses and features international co-direction: Dr. Eduardo Fernández, professor and director of the Institute of Bioengineering at UMH, has led the part related to visual restoration, while Dr. Giacomo Valle from Chalmers University of Technology (Sweden) has been responsible for the part concerning touch. Researchers from leading centers in sensory neuroprosthetics research in the United States and the Netherlands also participated.
