However, placement of the ABI is difficult and it has achieved limited performance levels (comparable with single-channel CIs) in its main target group of neurofibromatosis type II (NF2) patients ( Shannon et al., 1993 Lenarz et al., 2001 Otto et al., 2002). An alternative is the auditory brainstem implant (ABI). However, stimulation location along the ICC laminas affects response properties that have shown to be important for speech perception performance, and needs to be considered when implanting future AMI patients.Īlthough cochlear implants (CIs) can restore intelligible speech perception in patients with sensorineural hearing loss ( Rauschecker and Shannon, 2002 Skinner et al., 2002), they are ineffective for patients with severely damaged auditory nerves or unimplantable cochleas. The AMI will be implanted along the tonotopic axis of the ICC to achieve frequency-specific activation. These findings suggest that at least two spatially distinct functional output regions exist along an ICC lamina: a caudal–dorsal region and a rostral–ventral region. We also observed longer first spike latencies, which correlated with reduced spiking precision, when stimulating in more caudal and dorsal ICC regions. Our results indicate that stimulation of more rostral and somewhat ventral regions within an ICC lamina achieves lower thresholds, smaller discriminable level steps, and larger evoked potentials in A1. In this study, we electrically stimulated different regions along the isofrequency laminas of the ICC and recorded the corresponding A1 activity in ketamine-anesthetized guinea pigs using multisite probes to systematically assess ICC stimulation location effects. However, we also observed that stimulation location along the caudorostral (isofrequency) dimension of the ICC affects thresholds and frequency specificity in A1, suggesting possible differences in functional (output) organization within the ICC. We have previously shown that ICC stimulation achieves lower thresholds, greater dynamic ranges, and more localized, frequency-specific primary auditory cortex (A1) activation than CI stimulation. The inferior colliculus central nucleus (ICC) has potential as a new site for an auditory prosthesis for deaf patients who cannot benefit from cochlear implants (CIs).
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