A grand challenge for the 21st century will be to build an interface between our brains and electronic systems. Tom Kalil, Deputy Director for Policy for the White House Office of Science and Technology Policy, envisions this new world as one where “people with prosthetic legs climb mountains and people with prosthetic arms play the piano.” The robotic technology needed for such feats exists, as demonstrated by the DEKA Arm and others. However, what is lacking is a robust, high-performance signal from the brain to control these prostheses.
While brain-computer interface systems exist in prototype form, their performance is extremely limited. Currently, all devices that interface computers with the body use passive electrodes and require that each electrode be individually connected to remote electronics. Using this technology, it is impossible to build a high-resolution (<1 mm) interface over broad regions (8 cm × 8 cm) of the brain, since this would require an electrode array with thousands of sensors and corresponding wires to be individually connected in the limited space inside the skull. To overcome this limitation, we have developed new implantable electrode array technology that incorporates active, flexible silicon electronics. By moving the first stage of signal processing directly to the interface with the brain, we are no longer constrained by the requirement of connecting one wire for every electrode. Instead, we only need a single wire for each row and each column of the array. This dramatically reduces the wiring burden and enables thousands of electrodes that are connected with just a few wires.
We have demonstrated an extremely flexible array of 360 recording electrodes that integrates an amplifier and multiplexer directly under each electrode in a thin sheet of polyimide. These electrode arrays can sample micro-electrocorticographic (μECoG) signals from the surface of the brain at high temporal (>10 kHz/ channel) and high spatial resolution (<500 μm electrode spacing), while requiring only a few wires to be connected. Our most recent improvements in integration have enabled arrays of 1,024 multiplexed and amplified sensors, spaced as close as 250 µm apart. Further integration will soon yield thousands of sensors that are connected using just a few wires.
This technological innovation has opened the door to a new generation of brain-machine interfaces that use active, flexible electronics, to interface with the brain at 1000 times higher spatial resolution than today’s clinical devices. In our lab, we are currently using this new technology to develop 'smart neuroprosthetics' in three domains: motor control, sensory perception, and seizure management in patients with epilepsy. Our overall goal is a 'one size fits all,' general purpose, programmable device that can be easily adapted for use in various applications such as robotic arms that can be manipulated by tetraplegic patients, adaptive hearing aids that dynamically improve acoustics for people with hearing loss, or responsive neurostimulation to suppress seizures in patients with epilepsy. This technology opens a new window into understanding brain function, and enables truly high-performance brain-machine interfaces.