With Commentary from Professor Michael
The artificial electrical stimulation of neurons for the treatment of neurological disease and impairment is a well-established field that is undergoing rapid development in the treatment of diseases such as Parkinson’s disease, obsessive compulsive disorder, epilepsy,as well as auditory and visual impairments using cochlear and retinal implants. The basic principle underlying these treatments arises from the inherent electrical excitability of all neurons in the body. By using electrical impulses to stimulate neurons, we can attempt to manipulate their functions. Thus, if there is a dysfunction in the firing of some neurons in the network, we can seek to replace them using electrodes. Generally, this is an area of research only being explored in the context of the developed world, however, particularly in the case of cochlear implants, there may soon be an evolving role for artificial neural stimulation in the developing world.
To appreciate the potential of artificial neural stimulation, we must first appreciate the way in which the neural network operates. The communication between neurons within the brain is the primary control point of all human behaviours, ranging from the movement of our limbs to the control of our deepest thoughts and emotions. These neurons communicate via unique patterns of electrical activity within synchronousneuronal networks, which are composed of billions of cells. Different sensations and behaviours each depend upon a unique subset of neurons within this synchronous network for their function. For instance, the neurons recruited for vision differ in appearance, location, electrical signature, and distribution when compared to those required for hearing. However, when the health of these neurons is compromised, so too is their ability to produce these complex patterns of activity. Artificial neural stimulation takes advantage of the electrical potential of neurons, whose function is dependent upon the flow of charge from one cell to the next. By injecting such neurons with an electrical stimulus using electrodes, we can artificially generate new patterns of neuronal activity that can replace the role of any dysfunctional cells in the network.
Bionic vision is still in its infancy but has made significant strides in the treatment of retinitis pigmentosa, the leading cause of inherited pigmentosa, the leading cause of inherited blindness. There are also plans to utilise it for the treatment of macular degeneration, the leading cause of blindness in the developed world. A United States Food and Drug Administration (FDA) approved model, developed by Second Sight in the USA, has already been implanted in hundreds of patients for the treatment of retinitis pigmentosa, restoring ‘functional vision’ to its recipients.
Functional vision is significantly different from normal vision and relies on ‘phosphenes’ to produce visual percepts of the surrounding world. Phosphenes are ‘spots’ within the visual field that can be perceived as either light or dark, such that a recipient may be able to perceive a horizon, navigate a dining room table, or see obstacles on a street. Phosphene vision is distinct from normal vision, being unable to depict colour or fine detail, as well as being limited by the number of phosphenes that a patient can see. Each phosphene corresponds to an electrode that has been placed on the retina, so with more electrodes, the patient will be able to perceive more sections of the visual field distinctly. However, there are multiple limitations to achieving higher visual acuity with more electrodes within retinal prostheses such that phosphene vision remains ‘functional’ but rudimentary compared to normal human vision. Michael Ibbotson, Director of the National Vision Research Institute and Professor at The University of Melbourne believes that “the sky is the limit” when it comes to the potential of artificial neural stimulation. “Two key factors have driven the rapid expansion of bionics in recent years; the improvement of surgical techniques for implantation and the increased biocompatibility of the materials used. Recent advances have made it possible to both record from and stimulate neurons in different areas of the brain. For instance, we could record sensory neural information from one part of the brain and then feed it back into motor neurons to emulate more natural movements of the body.” “However, in many cases although we do not perfectly replicate the original neural network’s function, there are still significant positive outcomes for patients psychologically to have a lost sense restored.[10, 11] Despite the difficulty inherent in reading a text with bionic vision, patients would prefer to utilise that sense, which otherwise would be lost to them, rather than opt for an easier means of reading such as an audiobook.” What has been restored for these patients is much more than their sight or their hearing, but rather a restoration of their sense of self.
According to Professor Ibbotson, it seems possible that the future of bionics may expand well beyond the medical world, stating that “once it becomes normal within medicine, it would not surprise me if bionics became cosmetic”. As the technology develops and becomes normalised as a treatment for various impairments and diseases, the public may eventually see an opportunity for self-improvement through artificial neural stimulation. For instance, breast implantation was originally developed for mastectomy patients before it became one of the most popular cosmetic surgeries of the modern world.  “If it were possible to improve memory function by selectively stimulating memory circuits at particular times, this could dramatically change the way in which students approached education, as well as in the treatment of memory disorders”. Although it seems closer to science fiction than reality, the cosmetic use of artificial neural stimulation, if it were realised, would have the potential to increase the profitability of this technology. If this were the case, it may be possible to fund its use in less developed regions, where it is currently unavailable. The expanding range of pathologies that can be treated by neural stimulation is promising, particularly for the developed world, but its implementation in the developing world is far more complex. There are many obvious hurdles in utilising this technology beyond high-income countries. The first issue is the prioritisation of resources to ensure the greatest possible impact on public health outcomes. There are many other competing health priorities that require attention before advanced interventions to improve neurological health can be implemented.[14, 15] “The cochlear implant appears to be the exception to the rule” according to Professor Ibbotson. Since its initial clinical introduction for patients in 1985, the cochlear implant has undergone significant developments and is now widely utilised in the treatment of hearing impairment, particularly in paediatrics where its impact is more dramatic in younger brains due to increased neuroplasticity. The cochlear implant has also seen recent introductions into low and middle-income countries in South America, Egypt, India and China, where it has faced multiple ethical and practical challenges. However, recent studies have shown that its use can remain cost-effective, even in regions where there is a scarcity of health resources. This is largely due to both the use of low-cost materials and the high health benefit associated with hearing restoration in patients.
The health priorities of patients also need to be aligned with access to neural implants, regardless of the product’s availability. If patients do not feel the need for such health interventions, then such interventions are unlikely to be utilised. For instance, the cochlear implant is still met with some resistance in the deaf community due to the fear of compromising their cultural identity.  Visual impairment is one such example where there is a significant variation between the priorities of the developing world and the developed world. In low-income countries, cataracts are the leading cause of blindness,  whilst in the developed world, the leading cause of blindness is age-related macular degeneration.  Naturally, there is a gap in the prioritisation of treatment availability where surgical intervention is a successful treatment for cataracts but remains difficult to deliver to disadvantaged regions of the world. The treatment of age-related macular degeneration and other degenerative retinal diseases has inspired the development of the bionic eye, but is less likely to be considered a treatment priority for the developing world until it becomes far more affordable. Global health priorities are consistently evolving to reflect the needs of the wider population.
Although it may be in the distant future, the wider utility of artificial neural stimulation will remain unclear until the technology has sufficiently advanced. It will be important for patients to have an awareness and understanding of such technology in the future, so that it is more likely to be accepted as a potential treatment for future health initiatives.
At a recent public forum, Professor Ibbotson also reported that one of the primary concerns of the public surrounding the use of neural implants was the potential for ‘mind control’. This demonstrates a significant gap in the public’s understanding of what artificial neural stimulation aims to achieve, as well as what it is capable of.
The potential for this type of neural control is well beyond the capabilities of current technology, which aims to stimulate otherwise inactive local networks of the brain to restore a lost function such as vision or hearing. However, these patient concerns are still important to consider if such technology is ever to be widely implemented in medicine in the future. The human brain is infinitely complex and research is only recently gaining significant momentum in our understanding of its function.
The development of artificial neural stimulation is an expanding field for the treatment of degenerative neural diseases. Although this technology is in its infancy, it has enormous potential for public health outcomes in both the developed and developing worlds, which are yet to be fully realised. The range of pathologies treated with artificial neural stimulation is expanding as rapidly as our understanding of the brain itself, making the development of this research an important area to watch in the future of medicine.
Commentary and revisions provided by Professor Michael Ibbotson.
Meo, accessed from https://www.pexels.com/photo/photo-of-head-bust-printartwork-724994/
Conflict of interest
Stephanie Kirkby is currently working with the National Vision Research Institute on a followup project relating to her Honours research with Professor Michael Ibbotson.
1. Aviles-Olmos I, Kefalopoulou Z, Tripoliti E, Candelario
J, Akram H, Martinez-Torres I, et al. Long-term outcome of
subthalamic nucleus deep brain stimulation for Parkinson’s
disease using an MRI-guided and MRI-verified approach. J Neurol
Neurosurg Psychiatry. 2014; 85: 1419-25
2. Alonso P, Cuadras D, Gabriëls L, Denys D, Goodman W,
Greenberg BD, et al. Deep brain stimulation for obsessivecompulsive
disorder: a meta-analysis of treatment outcome and
predictors of response. PloS one. 2015;10(7): e0133591
3. Cukiert A, Cukiert CM, Burattini JA, Lima AM. Seizure
outcome after hippocampal deep brain stimulation in a
prospective cohort of patients with refractory temporal lobe
epilepsy. Seizure. 2014;23(1):6-9.
4. Mäki-Torkko EM, Vestergren S, Harder H, Lyxell B. From
isolation and dependence to autonomy–expectations before and
experiences after cochlear implantation in adult cochlear implant
users and their significant others. Disability and rehabilitation.
5. Hadjinicolaou AE, Meffin H, Maturana MI, Cloherty SL,
Ibbotson MR. Prosthetic vision: devices, patient outcomes
and retinal research. Clinical & Experimental Optometry.
6. Hartong DT, Berson EL, Dryja TP. Retinitis pigmentosa.
7. Wong WL, Su X, Li X, Cheung CMG, Klein R, Cheng C-Y, et
al. Global prevalence of age-related macular degeneration and
disease burden projection for 2020 and 2040: a systematic review
and meta-analysis. The Lancet Global Health. 2014;2(2):106-116
8. Second Sight Announces Record Number of Argus II
Retinal Prosthesis Systems Implants and Completes First-in-
Human Orion Cortical Implant [press release]. California: Second
9. Pérez Fornos A, Sommerhalder J, da Cruz L, Sahel JA,
Mohand-Said S, Hafezi F, et al. Temporal properties of visual
perception on electrical stimulation of the retina. Investigative
Ophthalmology & Visual Science. 2012;53(6):2720-31.
10. Duncan JL, Richards TP, Arditi A, da Cruz L, Dagnelie G,
Dorn JD, et al. Improvements in vision related quality of life in
blind patients implanted with the Argus II Epiretinal Prosthesis.
Clinical and Experimental Optometry. 2017;100(2):144-50.
11. Da Cruz L, Coley BF, Dorn J, Merlini F, Filley E, Christopher
P, et al. The Argus II epiretinal prosthesis system allows letter and
word reading and long-term function in patients with profound
vision loss. British Journal of Ophthalmology. 2013;97:632-6
12. Champaneria MC, Wong WW, Hill ME, Gupta SC. The
evolution of breast reconstruction: a historical perspective. World
journal of surgery. 2012;36(4):730-42.
13. Fagan JJ, Tarabichi M. Cochlear implants in developing
countries: practical and ethical considerations. Current opinion in
otolaryngology & head and neck surgery. 2018;26(3):188-9.
14. Allegranzi B, Kilpatrick C, Storr J, Kelley E, Park BJ,
Donaldson L, et al. Global infection prevention and control
priorities 2018–22: a call for action. The Lancet Global Health.
15. Chao TE, Sharma K, Mandigo M, Hagander L, Resch SC,
Weiser TG, et al. Cost-effectiveness of surgery and its policy
implications for global health: a systematic review and analysis.
The Lancet Global Health. 2014;2(6):334-45.
16. Goldblat E, Most T. Cultural Identity of Young Deaf Adults
with Cochlear Implants in Comparison to Deaf without Cochlear
Implants and Hard-of-Hearing Young Adults. The Journal of Deaf
Studies and Deaf Education. 2018;23(3):228-39.
17. Khairallah M, Kahloun R, Bourne R, Limburg H, Flaxman
SR, Jonas JB, et al. Number of people blind or visually impaired
by cataract worldwide and in world regions, 1990 to 2010.
Investigative ophthalmology & visual science. 2015;56(11):6762-
18. Lebedev MA, Nicolelis MA. Brain-machine interfaces:
From basic science to neuroprostheses and neurorehabilitation.
Physiological reviews. 2017;97(2):767-837.