The four-year project is being led by a team at Rice University in Texas as part of a wider DARPA-funded programme that is developing wearable interfaces for communicating with the brain.
“In four years, we hope to demonstrate direct, brain-to-brain communication at the speed of thought and without brain surgery,” said Rice’s Jacob Robinson, the lead investigator on the $18m project, which was announced on May 20, 2019 as part of DARPA’s Next-Generation Nonsurgical Neurotechnology (N3) program.
“Speed is key,” Robinson said in a statement. “We have to decode neural activity in one person’s visual cortex and recreate it in another person’s mind in less than one-twentieth of a second. The technology to do that, without surgery, doesn’t yet exist. That’s what we’ll be creating.”
Rice’s MOANA (magnetic, optical and acoustic neural access device) will test techniques that employ light, ultrasound or electromagnetic energy to read and write brain activity. Robinson said MOANA’s decoding and encoding technologies will employ viral vector gene delivery, a technology in clinical trials for treating macular degeneration. Genetic payloads, which differ for decoding and encoding, will be delivered with the help of ultrasound to select groups of neurons in 16 target areas of the brain.
To ‘read’ neural activity, the MOANA team will reprogram neurons to make synthetic proteins called calcium-dependent indicators that are designed to absorb light when a neuron is firing.
Rice co-investigator Ashok Veeraraghavan said red and infrared wavelengths of light can penetrate the skull, and MOANA’s device will utilise this. The optical subsystem will reportedly consist of light emitters and detectors arrayed around the target area on a skull cap.
“Most of this light scatters off the scalp and skull, but a small fraction can make it into the brain, and this tiny fraction of photons contain information that is critical to decoding a visual perception,” said Veeraraghavan. “Our aim is to capture and interpret the information contained in photons that pass through the skull twice, first on their way to the visual cortex and again after they are reflected back to the detector.”
MOANA’s photodetectors will be ultrafast and ultrasensitive: the former is important for ignoring light that scatters off the skull and instead capturing only those photons that have had enough time to travel all the way to the target area of the brain and back.
Veeraraghavan, Robinson and MOANA collaborators plan to use the detectors to develop ToFF-DOT (time-of-flight enhanced functional diffuse optical tomography) which constructs a real-time 3D image of what’s inside the body using visible light.
Robinson said neurons in the 16 target regions of the visual cortex are expected to show up darker than normal on ToFF-DOT scans when they are firing and their calcium-dependent indicator proteins are absorbing light. Interpreting the dynamic changes from dark to light in the target areas is what MOANA will do to ‘read’ neural activity.
In the brain receiving an image, MOANA would ‘write’ information to neurons that are reprogrammed to fire in response to magnetic signals. The gene therapy payload delivered to these neurons will create proteins that tether either naturally occurring or synthetic iron nanoparticles to ion channels inside the neurons. The release of calcium through these ion channels is what 'fires' a neuron, causing it to actively transmit an electrical impulse.
“We plan to use magnetic fields to heat the iron, which in turn will open the channel and fire the neuron,” Robinson said. “But it’s not enough to do that every second or two. Our system must respond in milliseconds for the receiver and perceiver to experience the perception close enough in time that it seems simultaneous.”