Detection of interaural time differences in the alligator.
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 micros contralateral, with a median ITD of 450 micros. Thus, crocodilians and birds employ similar algorithms for ITD detection, although crocodilians have larger heads.
Carr
Catherine E
CE
Department of Biology, University of Maryland, College Park, Maryland 20742-4415, USA. cecarr@umd.edu
Soares
Daphne
D
Smolders
Jean
J
Simon
Jonathan Z
JZ
D000161:Acoustic Stimulation / Q000379:methods; D000200:Action Potentials / Q000502:physiology*; D000489:Alligators and Crocodiles; D000818:Animals; D001306:Auditory Pathways / Q000033:anatomy & histology / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology*; D001933:Brain Stem / Q000033:anatomy & histology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009924:Organ Culture Techniques / Q000379:methods; D018408:Patch-Clamp Techniques / Q000379:methods; D013017:Sound Localization / Q000502:physiology; D013997:Time Factors