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The Journal of Neuroscience, June 24, 2009, 29(25):7978-7990; doi:10.1523/JNEUROSCI.6154-08.2009

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Behavioral/Systems/Cognitive
Detection of Interaural Time Differences in the Alligator

Catherine E. Carr,^1,2 Daphne Soares,² Jean Smolders,³ and Jonathan Z. Simon²

¹Department of Biology and ²Neuroscience and Cognitive Science Program, University of Maryland, College Park, Maryland 20742-4415, and ³Klinikum der J. W. Goethe Universität, Zentrum der Physiologie, 60590 Frankfurt am Main, Germany

Correspondence should be addressed to Catherine E. Carr, Department of Biology and Neuroscience and Cognitive Science Program, University of Maryland, College Park, MD 20742-4415. Email: cecarr{at}umd.edu

The auditory systems of birds and mammals use timing information from each ear to detect interaural time difference (ITD). To determine whether the Jeffress-type algorithms that underlie sensitivity to ITD in birds are an evolutionarily stable strategy, we recorded from the auditory nuclei of crocodilians, who are the sister group to the birds. In alligators, precisely timed spikes in the first-order nucleus magnocellularis (NM) encode the timing of sounds, and NM neurons project to neurons in the nucleus laminaris (NL) that detect interaural time differences. In vivo recordings from NL neurons show that the arrival time of phase-locked spikes differs between the ipsilateral and contralateral inputs. When this disparity is nullified by their best ITD, the neurons respond maximally. Thus NL neurons act as coincidence detectors. A biologically detailed model of NL with alligator parameters discriminated ITDs up to 1 kHz. The range of best ITDs represented in NL was much larger than in birds, however, and extended from 0 to 1000 µs contralateral, with a median ITD of 450 µs. Thus, crocodilians and birds employ similar algorithms for ITD detection, although crocodilians have larger heads.

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Received Dec. 25, 2008; revised May 2, 2009; accepted May 12, 2009.

Correspondence should be addressed to Catherine E. Carr, Department of Biology and Neuroscience and Cognitive Science Program, University of Maryland, College Park, MD 20742-4415. Email: cecarr{at}umd.edu

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