In our previous article, we introduced the notion of neuroengineering as a field that encompasses much more than merely linking brain and machine. Indeed, when we speak of the brain, we usually refer to the big blob of nervous tissue inside our skull, called the cerebrum. We can stretch this definition a bit, and include the cerebellum (meaning “small brain”), a smaller and anatomically distinct organ right below our “main brain”, the cerebrum, still inside our skull. However, the fact remains that this is but one part of the nervous system, a full organ system in its own right. Indeed, while the brain is the central processing unit (in computer engineering terminology), we’re forgetting about the wiring, namely the rest of the nervous system!
Acting as an information highway of sorts, the spinal cord, situated along our vertebral column, relays information to and from the brain. From the spinal cord, at the level of each individual vertebra, large spinal nerves take over, further splitting into a complex cascade of nerves that iteratively branch out from each other, innervating our entire body.
Neuroengineering, as a discipline, concerns itself with interfacing with the nervous system, not merely the brain. As such, the hardware device that senses neural activity or stimulates it can be placed not only around or inside the brain, but also the spinal cord or the nerves. This broader perspective of neuroengineering opens up many possibilities, as each implantation site has its advantages and disadvantages.
The nervous system is a hierarchical system, with information processing becoming more advanced as we move from the body along the nerves, through the spinal cord, to the brain. The more downstream neuroengineering intervenes, the more the implant makes use of the pre-existing processing machinery of the body. However, this comes at the cost of reduced versatility, making the implant suited only for specific purposes. Additionally, in some cases, downstream sites are not viable due to medical conditions: for instance, people with a destroyed retina usually receive an implant in the optic nerve instead.
So what can you do with neuroengineering outside of the brain? For starters, via spinal implants, you can enable spinal cord injury (SCI) patients to walk again. The pioneering research conducted by Prof. Gregoire Courtine and his team at the Federal Institute of Technology Lausanne (EPFL) constitutes a perfect example thereof, making [global headlines](Spinal implants let three people who were paralysed walk with support | New Scientist) every couple of years for achieving success in ever more high profile cases of SCI patients.
People who have lost limbs can regain them via robotic replacements connected to their unaffected nerves anterior to the site of the lost limb. Such devices are called neuroprosthetics and the neural interface itself is designated a [peripheral nerve interface (PNI)](Peripheral nerve interface – Wikipedia).
Finally, one of the more outlandish applications is in controlling the inner workings of the body, for instance the respiratory system. For instance, the [remede system](Central Sleep Apnea (CSA) Treatment | remedē® System (zoll.com)) from Zoll Medical is an implantable device that interfaces with the phrenic nerve to treat central sleep apnea (CSA), where the brain fails to send correct signals to the diaphragm for normal breathing during sleep. This is part of an emerging field called bioelectronic medicine (alternatively called electroceuticals), which can potentially treat, among other afflictions, chronic obstructive pulmonary disease (COPD) and type 1 diabetes. There’s even an eponymous scientific journal called [Bioelectronic Medicine](Bioelectronic Medicine | Home (biomedcentral.com)) that is devoted exclusively to this emerging field!
As we’ve now seen, neuroengineering is a far richer field than merely its famous centerpiece: brain-computer interfaces. We’re still only scratching the surface of the possibilities offered to us by neuroengineering and we will expound upon its merits, shortcomings and finer facets in other blog posts.