Functional auditory prostheses provide an information-carrying interface between electronic systems and neuronal systems. They provide coherent sensations of sound in patients suffering from profound (usually total) deafness as a result of various traumatic, infectious, and hereditary diseases that cause loss of the cochlear hair cells. These cells normally transduce the mechanical vibrations of sound waves (entering the fluid-filled cochlear chambers, via the middle ear ossicular chain) into bioelectric impulses to the brain. The axons of the spiral ganglion cells which make up the auditory nerve convey these impulses from the organ of Corti on the basilar membrane (where the hair cells are located) to the brain stem auditory nuclei. In the absence of the hair cells, the remaining spiral ganglion cells can be activated directly by electrical currents from stimulating electrodes either in or near the cochlear chambers (usually at the round window entrance or in the scala tympani) or in the auditory nerve proper as it courses through the bony modiolar canal. The auditory nerve activity so elicited is interpreted as sound by the central nervous system, with loudness, pitch, and timbre apparently dependent on the amplitude, location, and waveform of the stimulating current.