A wireless, ontogenetic device that sends information directly to the brain has been developed by a team at Northwestern University. The soft, flexible device sits under the scalp, on top of the skull, where it delivers precise patterns of light through the bone to activate neurons across the cortex.
“Our brains are constantly turning electrical activity into experiences, and this technology gives us a way to tap into that process directly,” said Yevgenia Kozorovitskly, PhD, professor of neurobiology at Northwestern University. “This platform lets us create entirely new signals and see how the brain learns to use them. It brings us just a little bit closer to restoring lost senses after injuries or disease while offering a window into the basic principles that allow us to perceive the world.
This work is published Nature Neuroscience in the paper, “Patterned wireless transcranial optogenetics generates artificial perception.”
The device’s patterned bursts of light activated specific populations of neurons—genetically modified to respond to light—deep inside the brains of mouse models. The mice quickly learned to interpret these patterns as meaningful signals, which they could recognize and use. Even without touch, sight, or sound involved, the animals received information to make decisions and successfully completed behavioral tasks.
The authors wrote that establishing a minimally invasive, wirelessly effective, and miniaturized platform with long-term stability is “crucial for creating research methods and clinically meaningful biointerfaces capable of mediating artificial perceptual feedback.”
Indeed, the technology has immense potential for various therapeutic applications, including providing sensory feedback for prosthetic limbs, delivering artificial stimuli for future vision or hearing prostheses, modulating pain perception without opioids or systemic drugs, enhancing rehabilitation after stroke or injury, controlling robotic limbs with the brain, and more.
The soft, flexible device conforms to the surface of the skull and shines light through the bone. “Red light penetrates tissues quite well,” Kozorovitskiy said. “It reaches deep enough to activate neurons through the skull.” The device features a programmable array of up to 64 micro-LEDs, so the number of patterns that can be generated with various combinations of LEDs (frequency, intensity, and temporal sequence) is incredibly high.
With real-time control over each LED, researchers can send complex sequences to the brain that may resemble the distributed activity that occurs during natural sensations. Because real sensory experiences activate distributed cortical networks—not tiny, localized groups of neurons—the multi-region design mimics more natural patterns of brain activity.
The team trained mice, which had been engineered to have light-responsive cortical neurons, to associate a particular pattern of brain stimulation with a reward. Typically, this task involved visiting a specific port in a chamber. In a series of trials, the implant delivered a specific pattern across four cortical regions. The mice quickly learned to recognize this target pattern among dozens of alternatives. Using artificial signals carried by the target pattern, they chose the correct port to receive a reward.
“Developing this device required rethinking how to deliver patterned stimulation to the brain in a format that is both minimally invasive and fully implantable,” said John Rogers, PhD, professor of materials science and engineering, biomedical engineering, and neurological surgery in the McCormick School of Engineering and Northwestern University School of Medicine.
“By integrating a soft, conformable array of micro-LEDs—each as small as a single strand of human hair—with a wirelessly powered control module, we created a system that can be programmed in real time while remaining completely beneath the skin, without any measurable effect on natural behaviors of the animals. It represents a significant step forward in building devices that can interface with the brain without the need for burdensome wires or bulky external hardware. It’s valuable both in the immediate term for basic neuroscience research and in the longer term for addressing health challenges in humans.”
Now the team plans to test more complex patterns and explore how many distinct patterns the brain can learn. Future iterations might include more LEDs, narrower spacing between LEDs, larger arrays covering more of the cortex, and wavelengths of light that penetrate deeper into the brain.
