For years, researchers have been exploring the potential for brain-computer interfaces (BCIs) – systems that connect up the human brain to external technology – to restore movement to people with paralysed limbs, using electrode arrays implanted directly on the brain's surface.
In the future, however, US government-backed research could enable the use of BCIs without any surgery at all – and they may first see use as a way of giving soldiers an advantage on the battlefield.
DARPA, the US military's R&D unit, which launched its Next-Generation Nonsurgical Neurotechnology (N3) program in 2018, is seeking to create non-invasive or minimally invasive brain-computer interfaces that could allow troops to communicate with systems from aerial vehicles or cyber-defense systems more quickly than they could with voice or keyboards; in short, soldiers could potentially fly drones or drive tanks with their thoughts alone.
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"DARPA is preparing for a future in which a combination of unmanned systems, artificial intelligence, and cyber operations may cause conflicts to play out on timelines that are too short for humans to effectively manage with current technology alone," said Al Emondi, the N3 program manager last year, when funding for six projects was announced: "By creating a more accessible brain-machine interface that doesn't require surgery to use, DARPA could deliver tools that allow mission commanders to remain meaningfully involved in dynamic operations that unfold at rapid speed."
The research agency has awarded funding to six groups under the N3 program, each investigating a different method of enabling humans and machines to communicate at thought-speed but without the need for surgery. The different groups are investigating a range of approaches; ultrasound, magnetic fields, light, electrical fields and optical tomography are among the technologies being researched.
Ohio-based R&D company Battelle is one of six groups to receive DARPA funding for a minimally invasive system that should eventually be able to gather and transmit information to soldiers' brains. "Imagine this: A soldier puts on a helmet and uses his or her thoughts alone to control multiple unmanned vehicles or a bomb disposal robot," as the company explained the project last year.
The aim of the project is "to enhance the capability of our military and our warfighters – to learn faster, do things better," Patrick Ganzer, principal research scientist at Battelle, told ZDNet.
The Battelle system is based on nanoparticles, and uses their electromagnetic properties to gather and communicate data to wearers.
The magnetic core of the particles would convert the neural electrical signals in the brain into magnetic ones that can be sent through the skull to the helmet-based transceiver worn by the user. The helmet transceiver could also send magnetic signals back to the particles where they would be converted to electrical impulses capable of being processed by the neurons – thus enabling two-way communication to and from the brain.
Battelle's nanoparticles will be injected into a vein or inhaled, and from there can be moved into the brain by a magnetic field. DARPA's requirements for positioning the BCI are very precise: Battelle will need to be able to site the particles within an area of 50 microns cubed – or about the width of one human hair.
As well as the nanoparticles inside the brain, the user will need to wear the helmet-style transceiver to send and receive the signals to external systems – and there are more limitations here. "The helmet has to be small, it can't be bulky, and it can't consume a lot of power," he says.
The main challenges to developing non-invasive or minimally invasive BCIs are, according to DARPA, overcoming the signal to noise ratio, and "the complex physics of scattering and weakening of signals as they pass through skin, skull, and brain tissue".
Battelle reckons the use of electromagnetic waves, rather than light or ultrasound, should overcome the problem. "The electromagnetic energy at low frequencies basically passes right through [the skull]. This is a big deal," Ganzer said.
Once N3 participants have worked out how to deal with the physics of the BCIs, DARPA says, they can proceed to work out how to code and decode neural signals, create a single device for sensing and stimulation, testing the safety and effectiveness of systems on animals, and then move on to trialling them in human volunteers.
While it's still unknown how the brain might react to thousands of nanoparticles being introduced, the use of other nanoparticles in medicine might provide some clues. Nanoparticles are already used in hospitals as part of 'contrast media', a substance that's injected or swallowed by patients to make particular parts of the body show up more clearly on a CT or MRI image.
However, contrast media is only supposed to be there for as long as it takes for the imaging to be completed; once it's over, the particles will be cleared from the body through the urine and faeces. Will it be possible to get the military-used nanoparticles to stay where they're put for as long as they're needed, and then removed from the body once their tour of duty is over?
"There's a clinical history of having these particles be introduced at non-toxic levels and being removed, which is great. We're drilling down into that – what's the density of particles? How many can we introduce safely? How fast are they removed? Can we accelerate the removal process? A lot of the experiments coming up are related to that, around safety and where do the particles end up," Ganzer says.
On the reverse side, the company is also looking at whether the time the particles spend inside the body can be extended. DARPA's challenge stipulates that the BCIs should be able to be used for two hours, but it's conceivable that real-world systems will need to be in situ for a lot longer to cope with long missions, potentially being reinjected or remagnetised to keep them in situ for more long-term use.
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Making a system that can work in the difficult environment of the human body is one thing, but making a BCI that can handle the complexity of human thought is another. Getting the interface for a minimally invasive system right is something of a Goldilocks challenge: too simple, and it's not useful; too complex and it's a pain for the user to manipulate.
"There's a trade-off between how complex feedback can be, and how fast you intuitively feel it. Imagine you have a very simple feedback system, let's say it's four locations, and each one means something different that you learn over time. If I increase that to eight or 20, or something more complex, I start to get put a lot of burden on the user. There's an operational sweet spot where it's easy to use, it doesn't take a lot of learning, and you don't have to think about it – it has this naturalness. Like any good technology, it just works," Ganzer said.
BCIs may be of interest to the military for their potential to help soldiers win battles, but much ground-breaking research around brain-computer interfaces is focused on medical applications. By bypassing broken connections in the pathways that lead from the brain to the muscles and skin, BCIs could help overcome paralysis and the loss of sense of touch that results from strokes and spinal-cord damage.
Such work typically involves invasive BCIs – systems that needs surgery to implant electrode arrays into the brain – but the new wave of non-invasive or minimally invasive systems could offer a non-surgical alternative in future. The prospect of a surgery-free alternative could also see BCIs be used in a broader range of conditions: Ganzer said as well as spinal injuries and strokes, minimally invasive systems could eventually also be used for epilepsy and depression.