**2. Overview of a cochlear implant system**

**Figure 2** shows the various components common to all of today's clinically applied cochlear implant systems. Sound is typically collected from microphones housed on a behind the ear (BTE) sound processor. The sound is first "cleaned" to remove noise and then processed to create the stimulation patterns destined for the implanted electrode array. Except in the case of one-piece processors, a lead connects the sound processor output to a radio frequency (RF) transmitter coil located above and behind the ear. The external coil is held in place over the implant's receiver coil through a pair of magnets: one external and one within the surgically implanted device under the skin. This arrangement supports reliable communication across the skin through the use of RF based telemetry. The RF signal provides both power for the implant's electronics and the information needed to produce electrical stimulation. Hence the implant consists of: its receiver coil, a hermetic package containing electronic circuits and an electrode lead assembly connecting to the electrode array that is placed inside the cochlea (**Figure 3**). In some of today's CI systems the sound processor and RF coil are a single component held in place by the magnet but having no wire or BTE part. This provides some esthetic advantage but may fall off more easily and compromises sound collection.

Additionally today's implants have the ability to make both physical and physiological measurements, using back-telemetry, to transmit these data to the sound processor. Through the use of wireless technology, information can be relayed to and from a host of devices: smartphones, tablets, laptops, remote microphones or other listening aids. Such connectivity leaves a CI user well placed to use many consumer devices to enhance their communication and support maintenance of their implant system.

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**Figure 3.**

**Figure 2.**

**3. Electrical stimulation principles**

*tympani with a mid-scala located electrode array.*

*(5) intra-cochlear electrode array and (6) the auditory nerve.*

In the earlier chapters of this book the auditory system has been described in some detail, including pathology that can result in the most debilitating degrees of hearing loss: severe to profound deafness. Fortunately, electrical stimulation can be delivered without external, middle or indeed even an inner ear. However, in the

*A cross-section through the spirally-shaped cochlea showing the various compartments, including the scala* 

*The components of a behind the ear (BTE) model of cochlear implant showing (1) the T-mic placed in the external ear canal, (2) BTE sound processor, (3) radio frequency transmitting headpiece, (4) the implant body,* 

*Electrical Stimulation of the Auditory System DOI: http://dx.doi.org/10.5772/intechopen.85285* *Electrical Stimulation of the Auditory System DOI: http://dx.doi.org/10.5772/intechopen.85285*

#### **Figure 2.**

*The Human Auditory System - Basic Features and Updates on Audiological Diagnosis and Therapy*

sounds, a reduction in the level of tinnitus and support of lip-reading with a reduction in the effort required for oral communication are all worthwhile benefits from use of a CI. It should also be noted that in many cases those most satisfied with their implant are not those who receive the highest scores on standardized tests of speech understanding. The following sections will describe how electrical stimulation of the auditory system is achieved, with the main focus being on CI systems. The factors that influence outcome, so far as they are known, will be described, along with the challenges in delivering clinical service, both today and into the future. With the future in mind the major research topics that are currently being addressed will be outlined.

*Percent correct scores on the CNC word test ranked from poorest to best for 113 cochlear implant users showing a* 

**Figure 2** shows the various components common to all of today's clinically applied cochlear implant systems. Sound is typically collected from microphones housed on a behind the ear (BTE) sound processor. The sound is first "cleaned" to remove noise and then processed to create the stimulation patterns destined for the implanted electrode array. Except in the case of one-piece processors, a lead connects the sound processor output to a radio frequency (RF) transmitter coil located above and behind the ear. The external coil is held in place over the implant's receiver coil through a pair of magnets: one external and one within the surgically implanted device under the skin. This arrangement supports reliable communication across the skin through the use of RF based telemetry. The RF signal provides both power for the implant's electronics and the information needed to produce electrical stimulation. Hence the implant consists of: its receiver coil, a hermetic package containing electronic circuits and an electrode lead assembly connecting to the electrode array that is placed inside the cochlea (**Figure 3**). In some of today's CI systems the sound processor and RF coil are a single component held in place by the magnet but having no wire or BTE part. This provides some esthetic

advantage but may fall off more easily and compromises sound collection.

Additionally today's implants have the ability to make both physical and physiological measurements, using back-telemetry, to transmit these data to the sound processor. Through the use of wireless technology, information can be relayed to and from a host of devices: smartphones, tablets, laptops, remote microphones or other listening aids. Such connectivity leaves a CI user well placed to use many consumer devices to enhance their communication and support maintenance of their implant system.

**2. Overview of a cochlear implant system**

*large variation in outcome reproduced from Holden et al. [79].*

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**Figure 1.**

*The components of a behind the ear (BTE) model of cochlear implant showing (1) the T-mic placed in the external ear canal, (2) BTE sound processor, (3) radio frequency transmitting headpiece, (4) the implant body, (5) intra-cochlear electrode array and (6) the auditory nerve.*

#### **Figure 3.**

*A cross-section through the spirally-shaped cochlea showing the various compartments, including the scala tympani with a mid-scala located electrode array.*
