Seite - 59 - in Cyborg Mind - What Brain–Computer and Mind–Cyberspace Interfaces Mean for Cyberneuroethics

Neuronal Interface Systems • 59 to the eardrum, the implants generate signals that are sent straight to the auditory nerve. In this way, they bypass the physical mechanism that pick up sound in normally hearing people, while, at the same time, circumvent- ing many of the problems that may develop in people who have difficulties in hearing. For first-time users, the response is instantaneous. Even people who have been deaf from birth have an immediate sensation that they may equate with sound, though quite what they are hearing is difficult to determine. The auditory nerve has about 30,000 axons (all associated with their respective neurons), which would normally be linked to individual hair cells. This accounts for a human being’s faculty to distinguish between very small differences in tone, as well as his or her ability to detect multiple frequencies all at once. However, with a cochlear implant, the entire bundle is stimulated by just twenty pins. Consequently, much of the detail will be lost. If the person was deaf since birth, another layer of uncertainty may exist, in that his or her auditory brain cortex will never have received a signal and will be untrained. The first neuronal implants have been remarkable, but current research is driven by a need to find new ways of making hundreds or thousands of con- nections with the auditory nerve, while making sure that those connections are stable. Currently, the twenty electrodes just sit within the nerve bundle and if they move a little, then it does not make too much difference. They were never located to a specific axon. However, if the number of connections goes up, then it will be important for movement to be reduced. Given that axons are fractions of a millimetre in size, the smallest movement could cause the electrode to move relative to the axon. Auditory Brainstem Implants A further step in the treatment of people with severe hearing loss is to bypass not only the outer, middle and inner ear, but also the auditory nerve itself. This is at an earlier stage of development, but neuronal inter- face implants, consisting of an array of very small electrode needles, have already been positioned directly into the auditory area of the brainstem of patients. The process requires surgery into the skull that is far more invasive than just placing the electrode on the cochlear nerve. At the moment, such implants are not as good at conveying sound as when cochlear nerve implants are used, but they can help a previously totally deaf person become more aware of everyday sounds. However, it can take months for the hearing area of the brain to learn to use this new input. At first, patients describe the sound as indefinite noises, but over time users can pick up a sensation of pitch and loudness. This open access edition has been made available under a CC-BY-NC-ND 4.0 license thanks to the support of Knowledge Unlatched. Not for resale.