The Making of a Cyborg #3: Neuroprosthetics

Cochlear implants can give people born deaf a sense of sound. (Photo by Bjorn Knetsch)

So far in this series I have primarily focused on how robotics can be used to replace missing limbs and assist movement, but the devices I have mentioned are, by and large, still very much external to the human body. This time I intend to delve deeper into the human body and discuss how computer technology can be integrated on a more fundamental level. This is the field of neuroprosthetics. A neuroprosthetic is, in a nutshell, "a device that supplants or supplements the input and/or output of the nervous system" [1], and while this field is too vast and complex to fully cover in a single blog post, I will do my best do give an overview of the major applications.

Perhaps the most widespread and well-established neuroprosthetic in use today is the cochlear implant, which can provide a representation of sound to the deaf. The device consists of a microphone placed just above the ear, as well as a speech processor that filters and adjusts the recorded sounds to provide better quality. A transmitter then converts the data from the speech processor into electrical impulses and sends them to an electrode array, which in turn sends these signals to different parts of the auditory nerve [2]. This final component plays the most important role in neuroprosthetics: connecting the nervous system to an external device.

Similar technology also exists to give blind people a degree of vision, though this is still very much a work in progress. The US company Second Sight has developed the Argus II Retinal Prosthesis System, which functions in a similar way to a cochlear implant [3]. A digital camera embedded in a pair of glasses sends image data to a video-processing microchip, which converts this data into electrical impulses. These impulses are then sent to a retinal implant, which consists of an array of 60 electrodes, which acts as a substitute for a normal retina -- the encoded pattern of light stimulates different parts of the implant which in turn sends different electrical signals to the brain's visual centre.

Electrodes attached to the brain can be used to transmit brain activity to computer devices. (Part of a larger illustration by Scott Leighton)

Neuroprosthetics can be broadly categorised into two types: those that collect information from the environment and send it to the brain (such as the above-mentioned cochlear and retinal implants), and those that read signals from the brain and convert them to external actions. Brain activity is typically measured via electrodes placed on or inside the brain, but signals can also be read via peripheral nerves not directly connected to the brain or spine. This can potentially be a much safer option, as surgery to install the technology is less risky and there is less danger of the body rejecting the implants and causing scarring in the brain. An example of neuroprostheses generating external actions is with robotic limbs, which is something I explored in an earlier instalment, but this interaction can work both ways: sensors on the surface of the limb can transmit signals back to the brain as a sense of touch [4].

These are just a few of the applications of neuroprosthetic technology -- there are many others currently in development. I haven't talked about devices that output brain signals to external devices in this post, and that's because this area has enough depth that it deserves an entry of its own. In the final instalment of "The Making of a Cyborg", I will provide an overview of brain-computer interfaces.

- Sam

Sources

[1] Leuthardt E, Roland J, Ray W. Neuroprosthetics [Internet]. The Scientist. 2014 [cited 20 October 2016]. Available from: http://www.the-scientist.com/?articles.view/articleNo/41324/title/Neuroprosthetics/

[2] Cochlear Implants [Internet]. National Institute on Deafness and Other Communication Disorders (NIDCD). 2016 [cited 20 October 2016]. Available from: https://www.nidcd.nih.gov/health/cochlear-implants

[3] Layton J. How does a "bionic eye" allow blind people to see? [Internet]. HowStuffWorks.com. 2007 [cited 20 October 2016]. Available from: http://health.howstuffworks.com/medicine/modern-technology/bionic-eye.htm

[4] Kwok R. Neuroprosthetics: Once more, with feeling. Nature [Internet]. 2013 [cited 20 October 2016];497(7448):176-178. Available from: http://www.nature.com/news/neuroprosthetics-once-more-with-feeling-1.12938