Auditory Neurophysiology, Neural Circuitry and Information Processing, and Computational Neuroscience
Research in the Auditory Processing Laboratory investigates the encoding, representation, and transformation of acoustic information within the auditory system. The goal is to understand how the brain represents and perceives the acoustic environment and how the neural systems in the brain are organized to create this representation. Our approach combines single- and multi-unit recording and analysis techniques, pharmacological manipulations, and computer modeling studies.
Current interest centers on the inferior colliculus (IC) because it occupies a pivotal position in the central auditory system; it receives direct inputs from most, if not all, of the auditory nuclei in the brainstem and, in turn, provides nearly all of the input to the auditory forebrain. Anatomical evidence suggests that the projections to the IC form highly organized synaptic domains with both segregated and shared sources of input. In support of this parallel processing model, our recent electrophysiological studies have discovered three principal IC response types that appear to be uniquely specialized for the neural encoding of spectral cues for sound localization, narrowband signals in noise, and binaural level and timing information. Based on correlations with response properties in lower-order nuclei, it has been hypothesized that each IC unit type reflects a dominant excitatory input from the medial superior olive, the lateral superior olive, or the dorsal cochlear nucleus. We are now performing experiments designed to provide direct evidence for these functional connections. In addition, we are exploring the functional consequences of this synaptic organization by comparing the quality of acoustic representations in IC target neurons and their sources of input. A question of particular interest in these latter experiments is how the ascending inputs to the IC interact with each other and a rich intrinsic inhibitory circuitry to enhance the processing of sound localization information.
DAVIS KA., RAMACHANDRAN R AND MAY BJ. Single unit responses in the inferior colliculus of decerebrate cats: II. Sensitivity to interaural level differences. J Neurophysiol 82: 164-175, 1999.
SPIROU GA, DAVIS KA, NELKEN I AND YOUNG ED. Spectral integration by type II interneurons in dorsal cochlear nucleus. J Neurophysiol 82: 648-663, 1999.
DAVIS KA AND YOUNG ED. Pharmacological evidence of inhibitory and disinhibitory neuronal circuits in dorsal cochlear nucleus. J Neurophysiol 83: 926-940, 2000.
RAMACHANDRAN R, DAVIS KA AND MAY BJ. Rate representation of tones in noise in the inferior colliculus of decerebrate cats. JARO 1: 144-160, 2000.
YOUNG ED AND DAVIS KA. Circuitry and function of the cat dorsal cochlear nucleus. In: Integrative Functions in the Mammalian Auditory Pathway, edited by D Oertel, R Fay and A Popper. Springer-Verlag, 2002, pp. 160-206.
DAVIS KA. Evidence of a functionally segregated pathway from dorsal cochlear nucleus to inferior colliculus. J Neurophysiol 87: 1824-1835, 2002.
DAVIS KA, RAMACHANDRAN R AND MAY BJ. Auditory processing of spectral cues for sound localization in the inferior colliculus. JARO 4: 148-163, 2003.
DAVIS KA. Contralateral effects and binaural interactions in dorsal cochlear nucleus. JARO 6: 280-296, 2005.
DAVIS KA. Spectral processing in the inferior colliculus. In: Auditory Spectral Processing, edited by M Malmierca and D Irvine. San Diego: Elsevier Inc, 2005, pp. 169-205.
DAVIS KA, LOMAKIN O AND PESAVENTO MJ. Response properties of single units in the dorsal nucleus of the lateral lemniscus of decerebrate cats. J Neurophysiol 98: 1475-1488 2007.
LOMAKIN O AND DAVIS KA. On the role of the wideband inhibitor in the dorsal cochlear nucleus: A computational modeling study. JARO 9: 506-520, 2008. PMCID: PMC2580807.