DOC PREVIEW
MIT HST 723 - Study Guide

This preview shows page 1-2-3-4-5 out of 14 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 14 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

jneurosci.orghttp://www.jneurosci.org/content/vol28/issue27/images/data/6914/DC1/supp2_08.gifhttp://www.jneurosci.org/content/vol28/issue27/images/data/6914/DC1/supp3_08.gifBehavioral/Systems/CognitiveInteraural Time Difference Processing in the MammalianMedial Superior Olive: The Role of Glycinergic InhibitionMichael Pecka,1,3Antje Brand,2Oliver Behrend,2and Benedikt Grothe1,2,31Division of Neurobiology, Department Biology II, Ludwig-Maximilians University Munich, D-82152 Martinsried, Germany,2Max Plank Institute ofNeurobiology, D-82152 Martinsried, Germany, and3Bernstein Center for Computational Neuroscience, D-81377 Munich, GermanyThe dominant cue for localization of low-frequency sounds are microsecond differences in the time-of-arrival of sounds at the two ears[interaural time difference (ITD)]. In mammals, ITD sensitivity is established in the medial superior olive (MSO) by coincidence detectionof excitatory inputs from both ears. Hence the relative delay of the binaural inputs is crucial for adjusting ITD sensitivity in MSO cells.How these delays areconstructed is, however, still unknown.Specifically, the question of whether inhibitory inputs are involved in timingthe net excitation in MSO cells, and if so how, is controversial. These inhibitory inputs derive from the nuclei of the trapezoid body, whichhave physiological and structural specializations for high-fidelity temporal transmission, raising thepossibilitythatwelltimedinhibitionis involved in tuning ITD sensitivity. Here, we present physiological and pharmacological data from in vivo extracellular MSO recordingsin anesthetized gerbils. Reversible blockade of synaptic inhibition by iontophoretic application of the glycine antagonist strychnineincreased firing rates and significantly shifted ITD sensitivity of MSO neurons. This indicates that glycinergic inhibition plays a major rolein tuning the delays of binaural excitation. We also tonically applied glycine, which lowered firing rates but also shifted ITD sensitivity ina way analogous to strychnine. Hence tonic glycine application experimentally decoupled the effect of inhibition from the timing of itsinputs. We conclude that, for proper ITD processing, not only is inhibition necessary, but it must also be precisely timed.Key words: sound localization; pharmacology; strychnine; population coding; superior oliviary complex; brainstemIntroductionAuditory space is synthesized by our brain based on one-dimensional movements of the two tympanic eardrums. Spectralcues and differences in level or arrival time of a sound at the twoears are used by the brain for performing this computational task.Interaural time differences (ITDs) are the dominant cue for lo-calizing low-frequency sounds, which are most important forlarger mammals (including humans) and small mammals livingin habitats that require detection of distant sounds and long-range communication (like Mongolian gerbils). These specieshave well developed low-frequency hearing and a well developedmedial superior olive (MSO) with principal neurons highly sen-sitive to ITDs (Goldberg and Brown, 1969; Moushegian et al.,1975; Crow et al., 1978; Yin and Chan, 1990; Spitzer and Semple,1995).Until recently, considerations of mammalian ITD processingwere dominated by a model proposed by Jeffress in 1948. Thismodel assumes coincidence detection of binaural excitatory in-puts with systematically varying axonal conduction time: Neu-rons respond maximally to ITDs that compensate for the differ-ences in axonal conduction time of the excitatory inputs fromboth ears. The systematic arrangement of axons with differentconduction times tunes neurons to different ITDs, creating aplace code whereby the location of peak activity forms a map ofauditory space. This arrangement has been verified both struc-turally and physiologically for the bird ITD detection system (forreview, see Carr and Soares, 2002; Grothe et al., 2004). Mammals,however, developed ITD processing independently (Manley etal., 2004) and the structural and functional mechanisms of ITDprocessing in mammals are not as well understood. Althoughfindings of anatomical studies in the cat seemed to be consistentwith a delay line organization for the contralateral excitatoryMSO inputs (Smith et al., 1993; Beckius et al., 1999), a number ofrecent studies indicate other or additional mechanisms underly-ing ITD tuning of MSO neurons and/or suggest a neuronal rep-resentation of ITDs that is different to the place coding in theJeffress model (for review, see Grothe, 2003; Palmer, 2004). Par-ticularly controversial is the role of synaptic inhibition in tuningMSO neurons to specific ITDs (Joris and Yin, 2007). There isanatomical (Clark, 1969; Perkins, 1973; Wenthold et al., 1987;Cant, 1991; Cant and Hyson, 1992; Kuwabara and Zook, 1992)and physiological evidence (Grothe and Sanes, 1993, 1994; Gro-the and Park, 1998) for strong glycinergic inputs onto MSO prin-cipal neurons. These inputs derive from the medial nucleus of theReceived Sept. 10, 2007; revised May 13, 2008; accepted May 23, 2008.This work was supported by The Max Planck Society (B.G.), the German Research Foundation (Deutsche For-schungsgemeinschaft)(Gr1205/12-1;GR1205/14-1,GRK 1091),and Bundesministeriumfu¨rBildung undForschung(Project 3.5 of the Bernstein Center for Computational Neuroscience). We thank Drs. D. H. Sanes, N. Lesica, D.McAlpine, and G. D. Pollak for helpful discussions and critical comments on this manuscript. We are thankful to Dr.R. M. Burger for technical advice. C. Schulte provided excellent assistance with the histology.Correspondence should be addressed to Prof. Dr. Benedikt Grothe, Department Biology II, Biocenter, Ludwig-MaximiliansUniversity Munich, GrosshadernerStrasse 2, D-82152Martinsried, Germany.E-mail: [email protected]. Brand’s present address: Helmholtz Zentrum Mu¨nchen–Deutsches Forschungszentrum fu¨r Gesundheit undUmwelt, GmbH, D-85764 Neuherberg, Germany.O.Behrend’s present address:Munich Center forNeurosciences–Brain and Mind,D-82152 Martinsried, Germany.DOI:10.1523/JNEUROSCI.1660-08.2008Copyright © 2008 Society for Neuroscience 0270-6474/08/286914-12$15.00/06914 • The Journal of Neuroscience, July 2, 2008 • 28(27):6914 – 6925trapezoid body (MNTB) and, to a lesser extent (Grothe andSanes, 1993), the lateral nucleus of the trapezoid body (LNTB).The MNTB in particular (von Gersdorff and Borst, 2002), butalso the LNTB (Spirou et al., 1998), show pronounced


View Full Document

MIT HST 723 - Study Guide

Download Study Guide
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Study Guide and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Study Guide 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?