ABSTRACT
Cochlear implants (CIs) are considered one of the most successful neural prostheses. Today about 500,000 severe-to-profoundly deaf individuals have received a CI to restore some of their hearing. While some patients communicate over the phone in different languages, others receive little benefit from CIs. For all of the users, however, noisy listening environments and music perception constitute a challenge. It has been argued that performance could be improved by reducing the interaction between neighboring electrode contacts and subsequently creating more independent channels for stimulation. More selective stimulation with electric current can be achieved through multipolar stimulation. Multiple electrode contacts are used to narrow the current field and to achieve more spatially selective stimulation (Bierer et al., 2002; Mens et al., 2005; Snyder et al., 2004; Srinivasan et al., 2010). A different approach to increase the number of different pitch percepts is current steering (Koch et al., 2006; Nogueira et al., 2017; Wu et al., 2016). Neighboring electrodes are used simultaneously to “steer” the current to selected neuron populations, which sit between the two stimulating electrodes to introduce virtual channels (Berenstein et al., 2008; Choi et al., 2009; Koch et al., 2006; Landsberger et al., 2009; van den Honert et al., 2007). More recently, the use of photons has been suggested as a novel approach to evoke responses from small populations of neurons (Boyden et al., 2005; Hernandez et al., 2014; Izzo et al., 2006a; Wells et al., 2005). Depending on the tissue, photons can be delivered without direct contact between the optical source and the target structure. Light beams can be focused, allowing for selective irradiation of neural tissue and introducing a larger number of independent channels for stimulation. The underlying assumption for favoring optical energy to stimulate neuron populations over electrical current relates to the finding that optical radiation can be delivered more selectively to groups of target neurons (Moreno et al., 2011; Richter et al., 2011a). It is anticipated that with optical stimulation, neural prostheses with enhanced neural fidelity can be developed. In this chapter, we discuss some design parameters required for an optical cochlear implant.
