Rewiring Vision

Authored By: Amy Li

Art By: Celine Shon

A Brain-Computer Interface (BCI) is a medical technology that enables communication between the neurosystem and an external device. This is done in three main steps: signal acquisition, signal processing, and device control [1]. First, in signal processing, microelectrodes can be implanted within the brain, where they record and measure neural activity. Second, in signal processing, raw signals are processed to filter out noise and identify clearer electrophysiological patterns. A computer (machine learning) algorithm can then undergo training to decode these brain signals into meaningful thoughts, movements, and commands- the signals are then sent to an external device, such as to a robotic limb or a computer, to execute a particular task of the user’s will. BCIs and microelectrode research is a subject highly curious to the general public, and have particular implications for enabling movement and communication for those suffering from motor neuron disease and paralysis. 

But what if BCI’s can also work backwards? When external visual signals instead are sent to implanted microelectrodes, neurons can also be stimulated. In a relatively new application, microelectrodes can connect to the brain’s visual cortex, helping visually impaired people to visualize shapes, colors, movement, and more – redefining the field of visual restorative medicine.

Globally, the prevalence of complete blindness is reported to be 43 million people [2], of which includes 1.4 million children [3] worldwide. In America, adults aged 40+ with uncorrectable vision issues are predicted to double, from 4 million in 2012 to 8 million by 2050. [4]. 

Eduardo Fernández et al., researchers from the University of Utah John A. Moran Eye Center, implanted a 96 electrode array into the visual cortex of a completely blind 57 year old patient. This microelectrode array, called the Utah Electrode Array (UEA), was special: it did not impair neural function in close proximity to the electrodes. These microelectrodes received visual signals through a video camera mounted on a pair of glasses, where the arrays then stimulated neurons within the retina to produce phosphenes- visualizations of lights and color when the eyes are closed. Lines and shapes could be perceived by the patient’s mind. During a 6 month series of experiments, no complications arose from the implantation surgery nor from neuron stimulation [5].

Regardless of the possibility of restoring vision through microelectrodes, ethical and legal considerations must be taken into account. Privacy and consent is a large issue with regards to brain activity and other personal neurological data, as potential misuse could reveal highly personal insights about an individual’s thoughts, health, and even mental states. Most importantly, long term patient safety must be continuously and extensively researched. Micromotion in the brain can cause electrodes to rip neural tissue apart [6]. 

On the technical side, inconsistencies between brain and electrode stiffness, as well as gradual isolation of electrodes from neurons over time [7], pose some of the most significant challenges; another barrier is poor neural tissue response to injury, which can deteriorate the long term function of the implanted microelectrode array [8]. In one cognitive study, Goss-Varley et al. found that “rats with chronically indwelling intracortical microelectrodes exhibited up to an incredible 527% increase in time to complete the fine motor task,” [9] revealing that the technology still has high risks in studies done in vivo.

Scientists from all over the world are experimenting with various applications of microelectrodes in the fight against blindness. Won Seo et al. showed that a square-frustum (imagine a square pyramid with the top sliced off), silicon-based microelectrode array was able to safely evoke spikes in retinal ganglion cells in vitro [10]. Rather than implants that target the visual cortex directly, retinal implants target the eye’s retina, and can act as an alternative area for microelectrode implantation. Other studies in animals have indicated the feasibility of implanting specialized microelectrode arrays [11]. 

However, many questions still remain unanswered: the visual system is incredibly complex, and thousands of signals are processed per second. Precisely how qualitative can we generate visual detail with the lowest opportunity costs? How can signals be more effectively filtered to create high resolution, full color vision? How will the brain and immune response adapt to artificial vision? And how long can microelectrodes stay within the brain or eye without compromising safety or efficacy?

The potential of vision restoration is extremely promising, and it will take time, and great collaborative research efforts, to implement the technology for communities who need them the most. 

References: 

1. Shih, J. J., Krusienski, D. J., & Wolpaw, J. R. (2012). Brain-Computer Interfaces in Medicine. Mayo Clinic Proceedings, 87(3), 268–279. https://doi.org/10.1016/j.mayocp.2011.12.008

2. Global Estimates of Vision Loss. (n.d.). The International Agency for the Prevention of Blindness. https://www.iapb.org/learn/vision-atlas/magnitude-and-projections/global/

3. Khabazkhoob, M., Yekta, A., Hooshmand, E., Saatchi, M., Ostadimoghaddam, H., Asharlous, A., & Taheri, A. (2022). Global prevalence and causes of visual impairment and blindness in children: A systematic review and meta-analysis. Journal of Current Ophthalmology, 34(1), 1. https://doi.org/10.4103/joco.joco_135_21

4. Blindness Facts, Statistics & Myths - Vision Center. (2023, July 11). https://www.visioncenter.org/resources/blindness-facts/

5. Fernández, E., Alfaro, A., Soto-Sánchez, C., Gonzalez-Lopez, P., Lozano, A. M., Peña, S., Grima, M. D., Rodil, A., Gómez, B., Chen, X., Roelfsema, P. R., Rolston, J. D., Davis, T. S., & Normann, R. A. (2021). Visual percepts evoked with an intracortical 96-channel microelectrode array inserted in human occipital cortex. Journal of Clinical Investigation, 131(23). https://doi.org/10.1172/jci151331

6. Duncan, J., Sridharan, A., Kumar, S. S., Iradukunda, D., & Muthuswamy, J. (2021). Biomechanical micromotion at the neural interface modulates intracellular membrane potentials in vivo. Journal of Neural Engineering, 18(4), 045010. https://doi.org/10.1088/1741-2552/ac0a56

7. HajjHassan, M., Chodavarapu, V., & Musallam, S. (2008). NeuroMEMS: Neural Probe Microtechnologies. Sensors, 8(10), 6704–6726. https://doi.org/10.3390/s8106704

8. Sharafkhani, N., Kouzani, A. Z., Adams, S. D., Long, J. M., Lissorgues, G., Rousseau, L., & Orwa, J. O. (2022). Neural tissue-microelectrode interaction: Brain micromotion, electrical impedance, and flexible microelectrode insertion. Journal of Neuroscience Methods, 365, 109388. https://doi.org/10.1016/j.jneumeth.2021.109388

9. Goss-Varley, M., Dona, K. R., McMahon, J. A., Shoffstall, A. J., Ereifej, E. S., Lindner, S. C., & Capadona, J. R. (2017). Microelectrode implantation in motor cortex causes fine motor deficit: Implications on potential considerations to Brain Computer Interfacing and Human Augmentation. Scientific Reports, 7(1). https://doi.org/10.1038/s41598-017-15623-y

10. Seo, H. W., Kim, N., Ahn, J., Cha, S., Goo, Y. S., & Kim, S. (2019). A 3D flexible microelectrode array for subretinal stimulation. Journal of Neural Engineering, 16(5), 056016. https://doi.org/10.1088/1741-2552/ab36ab

11. Rocca, A., Lehner, C., Wafula-Wekesa, E., Luna, E., Víctor Fernández-Cornejo, Abarca-Olivas, J., Soto-Sánchez, C., Fernández-Jover, E., & González-López, P. (2023). Robot-assisted implantation of a microelectrode array in the occipital lobe as a visual prosthesis: technical note. Journal of Neurosurgery, 1–8. https://doi.org/10.3171/2023.8.jns23772