Responses of dorsal cochlear nucleus single units to electrical pulse train stimulation of the auditory nerve with a cochlear implant electrode.

In response to 100-ms duration electrical stimulation within the range 50-400 pulses per second (pps), and at 1.6- to 2.4-mA stimulus current, a range of poststimulus time histogram (PSTH) patterns were observed from dorsal cochlear nucleus (DCN) units, they were usually primarylike, onset or "negative response" and occasionally buildup or pauser patterns. It appeared that the excitatory and suppressive processes, also termed neural drives, in response to 2.5-pps electrical stimulation were the main determinants of DCN unit responses to 50- to 400-pps stimulation. This was demonstrated by a model of DCN responses to electrical stimulation of the auditory nerve. The neural drives required to model the PSTH patterns were (i) an excitatory process with a latency of < 5 ms, (ii) a second excitatory process latency of 4.5-10 ms, (iii) a long acting suppressive process with a latency of < 15 ms and a duration of > 70 ms, (iv) a short acting suppressive response with a latency of 2.5-3.7 ms and a duration usually < 5 ms, but always < 20, and (v) a drive contributing spontaneous activity to the unit. In addition to these processes which were observed at 2.5 pps, an additional, transient suppressive process was postulated to operate only at 50-400 pps. It was postulated that the PSTH patterns observed were due to differences in the strengths of these drives between units.