title: Linear processing of interaural level difference underlies spatial tuning in the nucleus of the brachium of the inferior colliculus.
abstract: The spatial location of sounds is an important aspect of auditory perception, but the ways in which space is represented are not fully understood. No space map has been found within the primary auditory pathway. However, a space map has been found in the nucleus of the brachium of the inferior colliculus (BIN), which provides a major auditory projection to the superior colliculus. We measured the spectral processing underlying auditory spatial tuning in the BIN of unanesthetized marmoset monkeys. Because neurons in the BIN respond poorly to tones and are broadly tuned, we used a broadband stimulus with random spectral shapes (RSSs) from which both spatial receptive fields and frequency sensitivity can be derived. Responses to virtual space (VS) stimuli, based on the animal's own ear acoustics, were compared with the predictions of a weight-function model of responses to the RSS stimuli. First-order (linear) weight functions had broad spectral tuning (approximately three octaves) and were excitatory in the contralateral ear, inhibitory in the ipsilateral ear, and biased toward high frequencies. Responses to interaural time differences and spectral cues were relatively weak. In cross-validation tests, the first-order RSS model accurately predicted the measured VS tuning curves in the majority of neurons, but was inaccurate in 25% of neurons. In some cases, second-order weighting functions led to significant improvements. Finally, we found a significant correlation between the degree of binaural weight asymmetry and the best azimuth. Overall, the results suggest that linear processing of interaural level difference underlies spatial tuning in the BIN.
authors: Biomedical Engineering Department, Johns Hopkins University, Baltimore, Maryland 21205, USA. sslee1@jhmi.edu
authors: Sean J
authors: SJ
authors: Slee
authors: Eric D
authors: ED
authors: Young
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000200:Action Potentials / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology; D001931:Brain Mapping; D002144:Callithrix; D003463:Cues; D003576:Electron Transport Complex IV / Q000378:metabolism; D005072:Evoked Potentials, Auditory / Q000502:physiology; D005456:Fluorescent Dyes / Q000378:metabolism; D007839:Functional Laterality / Q000502:physiology; D007245:Inferior Colliculi / Q000166:cytology* / Q000502:physiology*; D016014:Linear Models; D009474:Neurons / Q000502:physiology*; D011930:Reaction Time; D013017:Sound Localization / Q000502:physiology*; D013028:Space Perception / Q000502:physiology*; D014851:Wakefulness
chemical_list: D005456:Fluorescent Dyes; D003576:Electron Transport Complex IV