| FM Velocity Selectivity in the Inferior Colliculus is Inherited from Velocity Selective Inputs and Enhanced by Spike Threshold. | |
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MedLine Citation:
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PMID: 21813749 Owner: NLM Status: Publisher |
Abstract/OtherAbstract:
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Frequency modulation (FM) is computed from the temporal sequence of activated auditory nerve fibers representing different frequencies. Most studies in the inferior colliculus (IC) inferred from extracellular recordings that the precise timing of non-selective inputs creates selectivity for FM direction and velocity (Andoni et al. 2007; Fuzessery et al. 2006; Gordon and O'Neill 1998). We recently reported that two additional mechanisms were more important than input timing for directional selectivity in some IC cells: spike threshold, and inputs that were already selective (Gittelman et al. 2009). Here, we show that these same mechanisms, selective inputs and spike threshold, underlie selectivity for FM velocity and intensity. From whole-cell recordings in awake bats, we recorded spikes and postsynaptic potentials (PSPs) evoked by downward and upward FMs that swept identical frequencies at different velocities and intensities. To determine the synaptic mechanisms underlying PSP selectivity (relative PSP height), we derived sweep-evoked synaptic conductances. Changing FM velocity or intensity changed conductance timing and size. Modeling indicated that excitatory conductance size contributed more to PSP selectivity than conductance timing, indicating that the number of afferent spikes carried more FM information to the IC than precise spike timing. However, excitation alone produced mostly suprathreshold PSPs. Inhibition reduced absolute PSP heights, without necessarily altering PSP selectivity, thereby rendering some PSPs subthreshold. Spike threshold then sharpened selectivity in the spikes by rectifying the smaller PSPs. This indicates the importance of spike threshold, and that inhibition enhances selectivity via a different mechanism than previously proposed. |
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Authors:
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Joshua X Gittelman; Na Li |
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Publication Detail:
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Type: JOURNAL ARTICLE Date: 2011-8-3 |
Journal Detail:
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Title: Journal of neurophysiology Volume: - ISSN: 1522-1598 ISO Abbreviation: - Publication Date: 2011 Aug |
Date Detail:
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Created Date: 2011-8-4 Completed Date: - Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 0375404 Medline TA: J Neurophysiol Country: - |
Other Details:
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Languages: ENG Pagination: - Citation Subset: - |
Affiliation:
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1University of Texas at Austin. |
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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