Abstract
Electrophysiological studies on duration-tuned neurons (DTNs) from the mammalian auditory midbrain have typically evoked spiking responses from these cells using monaural or free-field acoustic stimulation focused on the contralateral ear, with fewer studies devoted to examining the electrophysiological properties of duration tuning using binaural stimulation. Because the inferior colliculus (IC) receives convergent inputs from lower brainstem auditory nuclei that process sounds from each ear, many midbrain neurons have responses shaped by binaural interactions and are selective to binaural cues important for sound localization. In this study, we used dichotic stimulation to vary interaural level difference (ILD) and interaural time difference (ITD) acoustic cues and explore the binaural interactions and response properties of DTNs and non-DTNs from the IC of the big brown bat (Eptesicus fuscus). Our results reveal that both DTNs and non-DTNs can have responses selective to binaural stimulation, with a majority of IC neurons showing some type of ILD selectivity, fewer cells showing ITD selectivity, and a number of neurons showing both ILD and ITD selectivity. This study provides the first demonstration that the temporally selective responses of DTNs from the vertebrate auditory midbrain can be selective to binaural cues used for sound localization in addition to having spiking responses that are selective for stimulus frequency, amplitude, and duration.
Highlights
Neurons throughout the auditory pathway respond selectively to the frequency and amplitude of an auditory stimulus
Our results show that some duration-tuned neurons (DTNs) from the inferior colliculus (IC) of the big brown bat have responses that were selective to interaural level difference (ILD) and interaural time difference (ITD) binaural cues
We show that some DTNs from the IC of the big brown bat have responses that are selective to binaural ILD and ITD cues, suggestive of some role in sound localization
Summary
Neurons throughout the auditory pathway respond selectively to the frequency and amplitude of an auditory stimulus. The presence of DTNs in bats and the finding that neural tuning for stimulus duration generally matches echolocation vocalization duration has naturally led to the hypothesis that one function of DTNs is to encode echo duration changes while hunting (Ehrlich et al, 1997; Sayegh et al, 2011); DTNs have been reported from the auditory midbrain, thalamus, and cortex of non-echolocating animals (frog: Potter, 1965; Narins and Capranica, 1980; Leary et al, 2008; mouse: Brand et al, 2000; Xia et al, 2000; rat: Pérez-González et al, 2006; chinchilla: Chen, 1998; guinea pig: He, 2002; Wang et al, 2006; cat: He et al, 1997), and from the visual cortex of cats (Duysens et al, 1996). For a recent review on duration tuning in both echolocating and non-echolocating vertebrates, see Sayegh et al (2011)
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