title: The Role of Conduction Delay in Creating Sensitivity to Interaural Time Differences.
abstract: Axons from the nucleus magnocellularis (NM) and their targets in nucleus laminaris (NL) form the circuit responsible for encoding interaural time difference (ITD). In barn owls, NL receives bilateral inputs from NM, such that axons from the ipsilateral NM enter NL dorsally, while contralateral axons enter from the ventral side. These afferents act as delay lines to create maps of ITD in NL. Since delay-line inputs are characterized by a precise latency to auditory stimulation, but the postsynaptic coincidence detectors respond to ongoing phase difference, we asked whether the latencies of a local group of axons were identical, or varied by multiples of the inverse of the frequency they respond to, i.e., to multiples of 2π phase. Intracellular recordings from NM axons were used to measure delay-line latencies in NL. Systematic shifts in conduction delay within NL accounted for the maps of ITD, but recorded latencies of individual inputs at nearby locations could vary by 2π or 4π. Therefore microsecond precision is achieved through sensitivity to phase delays, rather than absolute latencies. We propose that the auditory system "coarsely" matches ipsilateral and contralateral latencies using physical delay lines, so that inputs arrive at NL at about the same time, and then "finely" matches latency modulo 2π to achieve microsecond ITD precision.
authors.affiliation: Department of Biology, University of Maryland, College Park, MD, USA. cecarr@umd.edu.
authors.forename: Catherine
authors.initials: C
authors.lastname: Carr
authors.affiliation: Cluster of Excellence "Hearing4all", University of Oldenburg, Oldenburg, Germany.
authors.forename: Go
authors.initials: G
authors.lastname: Ashida
authors.affiliation: Institute for Biology II, RWTH Aachen, Aachen, Germany.
authors.forename: Hermann
authors.initials: H
authors.lastname: Wagner
authors.affiliation: Institute for Theoretical Biology, Department of Biology, Humboldt-Universität zu Berlin, Berlin, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: McColgan
authors.affiliation: Institute for Theoretical Biology, Department of Biology, Humboldt-Universität zu Berlin, Berlin, Germany.
authors.forename: Richard
authors.initials: R
authors.lastname: Kempter
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D001369:Axons / Q000502:physiology; D009431:Neural Conduction; D011930:Reaction Time / Q000502:physiology*; D013017:Sound Localization / Q000502:physiology*; D020305:Strigiformes
keywords: Coding; Interaural time difference; Models; Plasticity; Rate