A developmental explanation of the dependence of binaural best delays on characteristic frequency
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ORAL PRESENTATION Open Access A developmental explanation of the dependence of binaural best delays on characteristic frequency Bertrand Fontaine 1,2 , Romain Brette 1,2* From Twentieth Annual Computational Neuroscience Meeting: CNS*2011 Stockholm, Sweden. 23-28 July 2011 Both mammals and birds use interaural time difference (ITD) as a cue to determine the horizontal position of a sound source in space. In the barn owl brainstem, neu- rons of the Nucleus Laminaris (NL) have firing curves which vary with the acoustic stimulus ITD. Each NL neuron is tuned to a certain ITD in that their response is maximal for a certain ITD, i.e., they respond prefer- ably when the stimuli from the two ears have a certain delay, called best delay (BD) of that neuron. Recently, it has been shown that the distribution of BDs along the tonotopical axis depends on the best frequency (BF) of their corresponding neurons. In particular, BDs rarely exceed 1/(2BF), an approximate constraint called the pi- limit. The origin of this BF-dependent distribution of BDs is still a matter of debate. In this work, we use a modeling approach to test whether the pi-limit could emerge from activity-driven plasticity, in particular Spike-Timing Dependent Plasti- city (STDP). Using a standard peripheral model and physiologically plausible spiking neuron models, we first feed binaural acoustic noise with ITDs in the physiologi- cal range of the barn owl (smaller than 250 μs) to NL neurons undergoing STDP and analyze the distribution of the resulting BDs. We show that STDP selects the inputs based on their synaptic delays and that the result- ing BD distribution mainly falls between plus or minus half the characteristic period of the corresponding neu- rons. We then use uncorrelated binaural white noises and show that the ITD selectivity and the dependence of binaural best delays on characteristic frequency also emerges after a simulated developmental period. We finally check that our conclusions also hold in more rea- listic settings, by feeding the model with real forest recordings. In conclusion, our results suggest that the frequency- dependence of BDs may simply be a by-product of the way ITD tuning develops in binaural neurons. It does not impair the ability of these neurons to represent the azimuth of sound sources, because BDs that differ by an integer number of characteristic periods are mostly redundant. Perhaps more interestingly, it also provides a complete representation of ITDs which is functional in any acoustical environment, even if the head of the ani- mal continues to grow after the critical development period. This suggests that the distribution of BDs does not simply mirror the statistics of binaural sounds dur- ing development, but instead provides a robust repre- sentation of changing environments. Acknowledgments This work was supported by the European Research Council (ERC StG 240132). Author details 1 Laboratoire Psychologie de la Perception, CNRS and Université Paris Descartes, 45, rue des Saints Pères, 75006 Paris, France. 2 Equipe Audition, Département d’Etudes Cognitives, Ecole Normale Supérieure, 29, rue d’Ulm, 75005 Paris, France. Published: 18 July 2011 doi:10.1186/1471-2202-12-S1-O10 Cite this article as: Fontaine and Brette: A developmental explanation of the dependence of binaural best delays on characteristic frequency. BMC Neuroscience 2011 12(Suppl 1):O10. * Correspondence: [email protected] 1 Laboratoire Psychologie de la Perception, CNRS and Université Paris Descartes, 45, rue des Saints Pères, 75006 Paris, France Full list of author information is available at the end of the article Fontaine and Brette BMC Neuroscience 2011, 12(Suppl 1):O10 http://www.biomedcentral.com/1471-2202/12/S1/O10 © 2011 Fontaine and Brette; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Transcript of A developmental explanation of the dependence of binaural best delays on characteristic frequency
ORAL PRESENTATION Open Access
A developmental explanation of the dependenceof binaural best delays on characteristicfrequencyBertrand Fontaine1,2, Romain Brette1,2*
From Twentieth Annual Computational Neuroscience Meeting: CNS*2011Stockholm, Sweden. 23-28 July 2011
Both mammals and birds use interaural time difference(ITD) as a cue to determine the horizontal position of asound source in space. In the barn owl brainstem, neu-rons of the Nucleus Laminaris (NL) have firing curveswhich vary with the acoustic stimulus ITD. Each NLneuron is tuned to a certain ITD in that their responseis maximal for a certain ITD, i.e., they respond prefer-ably when the stimuli from the two ears have a certaindelay, called best delay (BD) of that neuron. Recently, ithas been shown that the distribution of BDs along thetonotopical axis depends on the best frequency (BF) oftheir corresponding neurons. In particular, BDs rarelyexceed 1/(2BF), an approximate constraint called the pi-limit. The origin of this BF-dependent distribution ofBDs is still a matter of debate.In this work, we use a modeling approach to test
whether the pi-limit could emerge from activity-drivenplasticity, in particular Spike-Timing Dependent Plasti-city (STDP). Using a standard peripheral model andphysiologically plausible spiking neuron models, we firstfeed binaural acoustic noise with ITDs in the physiologi-cal range of the barn owl (smaller than 250 µs) to NLneurons undergoing STDP and analyze the distributionof the resulting BDs. We show that STDP selects theinputs based on their synaptic delays and that the result-ing BD distribution mainly falls between plus or minushalf the characteristic period of the corresponding neu-rons. We then use uncorrelated binaural white noisesand show that the ITD selectivity and the dependenceof binaural best delays on characteristic frequency alsoemerges after a simulated developmental period. We
finally check that our conclusions also hold in more rea-listic settings, by feeding the model with real forestrecordings.In conclusion, our results suggest that the frequency-
dependence of BDs may simply be a by-product of theway ITD tuning develops in binaural neurons. It doesnot impair the ability of these neurons to represent theazimuth of sound sources, because BDs that differ by aninteger number of characteristic periods are mostlyredundant. Perhaps more interestingly, it also provides acomplete representation of ITDs which is functional inany acoustical environment, even if the head of the ani-mal continues to grow after the critical developmentperiod. This suggests that the distribution of BDs doesnot simply mirror the statistics of binaural sounds dur-ing development, but instead provides a robust repre-sentation of changing environments.
AcknowledgmentsThis work was supported by the European Research Council (ERC StG240132).
Author details1Laboratoire Psychologie de la Perception, CNRS and Université ParisDescartes, 45, rue des Saints Pères, 75006 Paris, France. 2Equipe Audition,Département d’Etudes Cognitives, Ecole Normale Supérieure, 29, rue d’Ulm,75005 Paris, France.
Published: 18 July 2011
doi:10.1186/1471-2202-12-S1-O10Cite this article as: Fontaine and Brette: A developmental explanation ofthe dependence of binaural best delays on characteristic frequency.BMC Neuroscience 2011 12(Suppl 1):O10.
* Correspondence: [email protected] Psychologie de la Perception, CNRS and Université ParisDescartes, 45, rue des Saints Pères, 75006 Paris, FranceFull list of author information is available at the end of the article
Fontaine and Brette BMC Neuroscience 2011, 12(Suppl 1):O10http://www.biomedcentral.com/1471-2202/12/S1/O10
© 2011 Fontaine and Brette; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the CreativeCommons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andreproduction in any medium, provided the original work is properly cited.
