title: Synaptic mechanisms underlying interaural level difference selectivity in rat auditory cortex.
abstract: The interaural level difference (ILD) is a sound localization cue that is extensively processed in the auditory brain stem and midbrain and is also represented in the auditory cortex. Here, we asked whether neurons in the auditory cortex passively inherit their ILD tuning from subcortical sources or whether their spiking preferences were actively shaped by local inhibition. If inherited, the ILD selectivity of spiking output should match that of excitatory synaptic input. If shaped by local inhibition, by contrast, excitation should be more broadly tuned than spiking output with inhibition suppressing spiking for nonpreferred stimuli. To distinguish between these two processing strategies, we compared spiking responses with excitation and inhibition in the same neurons across a range of ILDs and average binaural sound levels. We found that cells preferring contralateral ILDs (often called EI cells) followed the inheritance strategy. In contrast, cells that were unresponsive to monaural sounds but responded predominantly to near-zero ILDs (PB cells) instead showed evidence of the local processing strategy. These PB cells received excitatory inputs that were similar to those received by the EI cells. However, contralateral monaural sounds and ILDs >0 dB elicited strong inhibition, quenching the spiking output. These results suggest that in the rat auditory cortex, EI cells do not utilize inhibition to shape ILD sensitivity, whereas PB cells do. We conclude that an auditory cortical circuit computes sensitivity for near-zero ILDs.
authors.affiliation: Institute of Neuroscience, University of Oregon, Eugene, Oregon; Department of Biology, University of Oregon, Eugene, Oregon;
authors.forename: Michael
authors.initials: M
authors.lastname: Kyweriga
authors.affiliation: Institute of Neuroscience, University of Oregon, Eugene, Oregon; Department of Human Physiology, University of Oregon, Eugene, Oregon; and.
authors.forename: Whitney
authors.initials: W
authors.lastname: Stewart
authors.affiliation: Institute of Neuroscience, University of Oregon, Eugene, Oregon;
authors.forename: Carolyn
authors.initials: C
authors.lastname: Cahill
authors.affiliation: Institute of Neuroscience, University of Oregon, Eugene, Oregon; Department of Psychology, University of Oregon, Eugene, Oregon wehr@uoregon.edu.
authors.forename: Michael
authors.initials: M
authors.lastname: Wehr
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001303:Auditory Cortex / Q000502:physiology*; D008839:Microelectrodes; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000502:physiology; D018408:Patch-Clamp Techniques; D017207:Rats, Sprague-Dawley; D013017:Sound Localization / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*
keywords: auditory cortex; interaural level difference; sound localization; synaptic inhibition; voltage-clamp