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The Journal of Neuroscience, August 8, 2007, 27(32):8733-8743; doi:10.1523/JNEUROSCI.5127-06.2007
Behavioral/Systems/Cognitive
Spatially Distinct Functional Output Regions within the Central Nucleus of the Inferior Colliculus: Implications for an Auditory Midbrain Implant
Hubert H. Lim andDavid J. Anderson Kresge Hearing Research Institute, Department of Biomedical Engineering, and Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109
Correspondence should be addressed to Dr. David J. Anderson, Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, MI 48109-2122. Email: dja{at}umich.edu
The inferior colliculus central nucleus (ICC) has potential as a new site for an auditory prosthesis [i.e., auditory midbrain implant (AMI)] for deaf patients who cannot benefit from cochlear implants (CIs). 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. 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. 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. 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. We also observed longer first spike latencies, which correlated with reduced spiking precision, when stimulating in more caudal and dorsal ICC regions. 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. The AMI will be implanted along the tonotopic axis of the ICC to achieve frequency-specific activation. 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.
Key words: auditory cortex; auditory midbrain implant; auditory pathways; deep brain stimulation; inferior colliculus; isofrequency
Received Nov. 27, 2006; revised June 1, 2007; accepted June 25, 2007.
Correspondence should be addressed to Dr. David J. Anderson, Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, MI 48109-2122. Email: dja{at}umich.edu
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