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DARPA, ever riding the bleeding edge of technology, has announced a new program focused on designing tiny implanted electronics to treat medical conditions with by stimulating the peripheral nervous system with tiny implanted machines. Coming from the agency that helped create the internet, and has quietly fostered the incredible progress in prosthesis tech over the last decade, there may be reason to get excited.Neuromodulation, the primary technology under investigation, attempts to monitor and influence the peripheral nervous system. In order to make the potential of this kind of technology more concrete, an explanation of how the body self-regulates may be helpful. Many bodily functions use homeostatic control to keep some parameter within a healthy range, be it pupil response, hunger/satiety, or blood sugar levels.

The minimum requirements for such homeostatic regulation of a body system are a sensor to detect the environment, and an effector to move the system towards an ideal state; taken together these two parts make a negative feedback loop that keep the system near whatever the ideal state is. An example of such homeostatic feedback is temperature regulation, where an area in the brain called the hypothalamus receives sensory input from the peripheral nervous system about external temperature and sends involuntary output commands (sweating if it’s hot, hairs stand on end, muscles shiver if it’s cold) to keep the body at the right temperature.

Many physiological disorders result from the breakdown of homeostatic feedback – some part of the system is broken, and either improperly senses body condition or doesn’t respond. DARPA stated that their goal for the ElectRX program is to develop implants small enough to target individual nerve fibres, bridging gaps in a homeostatic loop where native biological parts are malfunctioning.

Neuromodulation technology does exist today, as evidenced by implanted pacemakers to restore cardiac function and deep brain stimulators (DBS) to sense and quash epileptic activity before it snowballs into a seizure. Existing tech is too bulky and not fine tuned enough for DARPA’s purposes though, with devices around the size of a pack of cards or your average smartphone. The agency says they’re seeking to “create ultraminiaturized devices, approximately the same size as individual nerve fibers, which would require only minimally invasive insertion procedures such as injectable delivery through a needle”.

That’s quite a jump – for reference, an implant the size of the largest type of nerve (A-alpha fiber) would be ~0.6cm3 in volume, vs. the ~85cm3 of an average pack of cards (or current peripheral implant), more than two orders of magnitude smaller. Clearly there is a lot of work to be done, but if anyone is cut out for the job it’s probably DARPA.

Speaking of DARPA, there is one other factor about the ElectRX program that the agency seems to be keeping under wraps – it’s potential military uses. Being that one of DARPA’s explicit missions is to maintain US military technological advantage, it’s hard to imagine defense applications being neglected during development, no matter how altruistic the project’s stated goal is. Viewed optimistically, implants developed in the ElectRX program could manipulate physiological state to make more effective soldiers; stimulators targeting the nerve that innervates the adrenal gland could create an ‘on demand adrenalin-rush’ in combat situations, or sensors that detect massive trauma in a limb and seal off arteries above the wound, for instance. Less optimistically, the technology could open a terrifying new world of torture techniques (by stimulating nerves that transmit pain to the brain) and ethically dubious behavioral engineering à la MKUltra.

The potential risks and rewards of ElectRX may sound like science fiction, but if DARPA succeeds even partially over the next few years they will be very much in the realm of reality. As such it’s best to put serious thought into both as the technology matures, so when it arrives we are not scratching our collective heads and wondering “where do we go from here?”


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