Neuroprosthetics: The Journey So Far

There's been a lot of fuss about the dangers lurking within the advancement in tech, and the impact it can have in various fields across the human-job-sphere. Well, evidently so due to the recent loss of jobs for 'manual workers' or carefully put, displacement of most manual workers with machines.

However, we can not ignore the formidable synergy from the man/machine merger that has pierced into uncharted historical territories, pushing the frontier of innovation, imagination, and human possibilities. This synergy is the birthplace of almost every breathtaking innovation. Among several realms of scientific innovations being birthed, only a few fields hold as much intrigue and promise as neuroprosthetics. Neuroprosthetics can be seen as one of the perfect scenarios where technology heavily overlaps medicine as it pushes the bandwidth of possibilities even further.

Stephen Hawking once opined,

We are all now connected by the Internet, like neurons in a giant brain

But with the advent and advancement of neuroprosthetics, it is evident that this connection is becoming more literal than metaphorical.

What is Neuroprosthetics?

Neuroprosthetics is an intersectoral field of neuroscience and engineering that employs technological innovation with scientific baselines to develop devices that can restore the lost function of the nervous system.

These devices called Neuroprostheses can restore or modulate varieties of neurally-mediated functions for the treatment of a range of conditions caused by neurodegenerative diseases, congenital anomalies, infections, and accidents. These conditions include spinal cord injury, Parkinson's disease, stroke, blindness, deafness, and others caused by accidents and attacks on the battlefield.

History of Neuroprosthetics

We can not categorically pinpoint the genesis of neuroprosthetics but history has a record of ancient Egyptians using leather and wood to construct artificial limbs as far back as 950 B.C. Several other prostheses like the Cairo Toe (700-950 B.C.), the Cartonnage Toe ( 600 B.C. ), and the Roman artificial leg (300 B.C. ) were discovered in ancient tombs and graveyards. In retrospect, it can be observed that ancient scientific knowledge was limited to artificial limb construction. However, this was a building block for a more sophisticated system as presented today.

To understand how we got to this level of sophistication, it is pertinent to lean back to memory lane and understand the chronological progression of neuroprosthetics. The following are some major historical strides in neuroprosthetics:

• 1579 - Ambroise Paré designed prosthetic limbs with mechanical components

• 1791 - Lurgi Galvani discovered that electrical stimulation of the nerve can use muscle contraction. This discovery was a huge milestone in the study of the nervous system, laying the framework for the creation of neuroprosthetics.

• 1860s - Gustav Fritsch and Eduard Hitzig via an experiment discovered that electrical stimulation of a certain part of the cerebrum causes involuntary muscular contractions of specific parts of the body. This discovery paved the way for advancement in BCIs.

• 1950s - José Manuel Rodriguez Delgado orchestrated the brain electrode implantation that uses electricity to stimulate specific brain areas for the treatment of epilepsy and other types of mental conditions.

• 1957 - The creation of the first cochlear implant as a hearing aid.

• 1960 - Testing and subsequent commercialization of neuroprosthesis for the treatment of drop-foot.

• 1977 - The development of the first Auditory Brainstem Implant (ABI) for deaf patients who are not eligible for cochlear implants.

• 1981 - Implantation of a peripheral nerve bridge in the spinal cord of a rat as a conduit for regenerating nerve fibers.

• 1988 - Development of the lumbar anterior root implant and Functional Electrical Stimulation (FES) for the treatment of paraplegia.

• 1990 - Approval of the first Cochlear implant in children by FDA.

• 1999 - John Chapin and his team experimented to demonstrate the feasibility of using brain activity for real-time control by simultaneous neuronal population recordings in experimental rats.

• 2010s - The development of close-looped neuroprosthetics that allowed for more effective and precise control of neuroprosthesis.

  
  

The 21st century has undoubtedly witnessed astronomical-paced development in neuroprosthetics, as there have been several remarkable advancements and sophistication of BCIs and other neuroprosthetics.

For instance;

• The development of Brain-controlled robotic limbs for individuals with limb amputations.
• The design of retinal implants and visual neuroprosthetics to restore vision.
• The ongoing development of neurotrophic factors which are proteins predicted to be a potent treatment of spinal cord injuries and other neurological disorders by facilitating and enhancing the growth of neurons.
• The ongoing development of a novel type of BCI called Neural Dust anchored by Elon Musk’s Neuralink.

Classes of Neuroprotheses

Neuroprotheses are classified into two classes which include implantable and non-invasive neuroprotheses.

• Implantable Neuroprotheses: These devices are surgically buried in the body for direct interaction with the spinal cord, brain, peripheral nerves, or at times the entire nervous system. The design of these devices enables them to either record neural activities in the nervous system, stimulate neurons, or foster communication between neural circuits and external devices. Examples include brain stimulators, cochlear implants, retinal prostheses, and others.

  
  

• Non-Invasive Neuroprotheses: These are brain-computer interface and myoelectric prostheses which are worn on the body and as such do not have any direct interaction with the nervous system.

Types of Neuroprostheses

All types of neuroprostheses share a similar mode of operation irrespective of their type. They create a neural link between the brain and a computer, enabling a patient to use his/her nervous system to control sensory organs or limbs. The primary types of neuroprostheses include the sensory, motor, and neuromodulation neuroprostheses.

Sensory Neuroprostheses

These types of devices convert light, sound, and other physical stimuli to electrical signals that the brain can interpret to enhance lost sensory modalities. Examples of Sensory neuroprostheses include:

• Visual Prostheses: These devices stimulate the photoreceptor cells in the degenerated retinal cells to send visual information to the brain. Example: the retinal implants.

• Auditory Prostheses: These devices bypass the damaged cochlea and directly stimulate the auditory nerves to enable the patient to hear sounds. Example: Cochlear implants

Motor Neuroprostheses

These devices interpret the patient’s intended movements via signals from the muscle or brain to act. Examples of Motor prostheses include:

• Prosthetic Limbs: Controlled by the myoelectric signals, prosthetic limbs are artificial limbs that replace missing or amputated body parts to provide mobility and support. They are mechanical devices that get electrical signals from the user’s muscles via the myoelectric signals to control movements.

  
  

• Functional Electrical Simulation (FES) Devices: These are electrodes that utilize electrical currents to stimulate muscles and nerves directly to enhance or restore the functions of the muscles and nerves marred by neurological conditions or perhaps paralysis. These electrodes are placed externally on the skin or implanted surgically into the skin. Paralytic patients on FES devices can move their limbs with ease.

  
  

• Brain-Computer Interfaces (BCIs): These are implantable neuroprostheses that use brain signals to enable users to control external devices like wheelchairs or robotic arms. These devices work by capturing and analyzing the electrical activities of the brain’s neurons and utilizing this information to control external devices. BCI can also be non-invasive like Electroencephalography (EEG) which is used to record signals from the scalp.

Neuromodulation Neuroprosthetics

These devices use electrical signals to regulate and modulate the activities of the nervous system to treat a plethora of abnormalities like neurological diseases, movement disorders, and diseases.

Examples of these devices include;

• Deep Brain Stimulators (DBS): These are brain implantable devices that deliver electrical stimulation to specific areas to modulate neural activities in these areas. They are used to treat a variety of conditions including dystonia, Parkinson’s disease, essential tremor, obsessive-compulsive disorder (OCD), major depressive disorder (MDD), and Tourette syndrome.

  
  

• Transcranial Magnetic Stimulators (TMS): They are non-invasive neuromodulation devices that use strong magnetic fields to stimulate brain nerve cells. They treat medical conditions such as depression, anxiety, PTSD, OCD, and migraines.

  
  

• Spinal Cord Stimulator: This device mimics the spinal cord by modulating the signal transmitted between the brain and the body and sending the same to the spinal cords to aid people with spinal injuries and to treat chronic pains like neuropathic pains and back pains.

  
  

• Vagus Nerve Stimulators (VNS): These devices are implanted in the vagus nerve to stimulate this nerve to treat conditions such as epilepsy, depression, and migraine. The Vagus nerve connects the brain to the rest of the body and plays an active role in regulating various functions in the body.

  
  

• Peripheral Nerve Stimulators (PMS): These devices are implanted next to one of the peripheral nerves. They function by using electric currents to alter the central processing of pain signals for the treatment of total knee arthroplasty, chronic knee pains, and back pain.

  
  

• Closed-loop neuroprosthetics: These devices establish bi-directional communication (that is: a real-time sensing and feedback mechanism) with the nervous system to enable a deeper level of interaction for a more precise neuromodulation. An example is a Responsive Neurostimulation (RNS) Device used on epileptic patients to prevent seizures.

Ethical Consideration in Neuroprosthetics

Neurodiversity is defined as the variation in neural and mental functions arising naturally from the interactions between genetic, neurobiological, and environmental factors. These functions are believed to exist on a spectrum that ranges from the normal to the abnormal.

While some regard functions in the abnormal axis as disabilities, others choose to perceive them as identities that should be recognized, respected, and preserved. This viewpoint is premised on the fact that a person with abnormal (pathological, to be precise) neural sense has created a world around the abnormality. Besides, it is believed that the absence of a sensory capability triggers a supernatural functionality of one or more sensory capabilities to compensate for this loss. In an instance where the lost sensory capability is restored, it is difficult to adequately predict the effect this will have on the already enhanced capacities.

Moreover, the radical psychological and lifestyle adjustment necessary for the integration into a new experiential world might be difficult as the patient has to reshape his perception of the world and other realities he was previously denied. This is why critics argue that to measure the entire worth of the prosthesis, psychological, social, and cultural elements related to a sensory capability must be examined alongside the neurophysiological ability to use that sense organ.

Although neurodiversity is usually mentioned in the debate on the use of neuroprosthetics on patients with autism spectrum disorder to modulate neural circuits, its core values and concepts can be stretched to cover other neurological and psychiatric conditions. For conditions such as bipolar or unipolar, patients may choose to resist treatment and identify with the cognitive and affective states of the disorder. This identification is believed to have influenced legal reasons against forcibly using neuroprosthetics or psychotropic drugs to treat symptoms of these disorders.

For neuromodulating prosthetics like DBS, BCI, and Hippocampal prosthetics, controlling symptoms is not the only assessment metric to quantify its effectiveness. Other factors such as the patient's overall experience after using the prosthetics are also considered.

In using DBS to treat psychiatric disorders, there have been ethical concerns and questions such as;

• Did the person receiving the treatment give consent to undergo the procedure?
• During the modulation of an unconscious patient’s mental function, who is the supreme controller of the patient’s action? The patient or the machine?
• Is the patient still acting in his free will?
• How detrimental or beneficial are the neural changes induced by DBS? What is the net gain or net loss?

In the case of using BCIs to treat a variety of neurological disorders, which is basically by predicting the intended action of the patients, several authors and researchers have expressed concerns about behavior control. The questions border on the free will of the patients and the algorithm’s functionality to follow the patient’s intentions to the latter.

Another general concern stems from the fear that this level of development prevalent in the neuroprosthetic field catalyzed by the advancement in AI, will birth ultra-sophisticated neuroprosthetics that will replace the neural circuit in the brain, making the brain a completely artificial organ. The implication of this can not be overestimated as humans can easily be turned into cyborgs, a stage no one wants to get to. Therefore while neuroprosthetics is gradually advancing its capabilities to completely eradicate neural disorders, there is a need to develop and implement stringent measures of laid-down principles and ethical guidelines to streamline and curb its possibilities of impending doom.

End Notes

For the past 5 centuries, neuroprosthetics has experienced tremendous evolution from being a practice revolving around a set of crude and rudimentary mechanical devices to highly advanced technologies and innovations that directly interfere with the nervous system. These advancements have improved the quality of life for individuals with disabilities and continue to hold promise for the future, as interdisciplinary research, deep work, and technological innovations propel the field forward. Though not without challenges, this field of science and technology has shown intriguing possibilities for a new reality.