The inferior colliculus (IC) receives ascending excitatory and inhibitory inputs from multiple sources, but how these auditory inputs converge to generate IC spike patterns is poorly understood. Simulating patterns of in vivo spike train data from cellular and synaptic models creates a powerful framework to identify factors that contribute to changes in IC responses, such as those resulting in age-related loss of temporal processing. A conductance-based single neuron IC model was constructed, and its responses were compared to those observed during in vivo IC recordings in rats. IC spike patterns were evoked using amplitude-modulated tone or noise carriers at 20–40 dB above threshold and were classified as low-pass, band-pass, band-reject, all-pass, or complex based on their rate modulation transfer function tuning shape. Their temporal modulation transfer functions were also measured. These spike patterns provided experimental measures of rate, vector strength, and firing pattern for comparison with model outputs. Patterns of excitatory and inhibitory synaptic convergence to IC neurons were based on anatomical studies and generalized input tuning for modulation frequency. Responses of modeled ascending inputs were derived from experimental data from previous studies. Adapting and sustained IC intrinsic models were created, with adaptation created via calcium-activated potassium currents. Short-term synaptic plasticity was incorporated into the model in the form of synaptic depression, which was shown to have a substantial effect on the magnitude and time course of the IC response. The most commonly observed IC response sub-types were recreated and enabled dissociation of inherited response properties from those that were generated in IC. Furthermore, the model was used to make predictions about the consequences of reduction in inhibition for age-related loss of temporal processing due to a reduction in GABA seen anatomically with age.
Keywords: aging, neuron, inhibition, amplitude modulation, auditory, GABA, lateral lemniscus, superior olive
Citation: Rabang CF, Parthasarathy A, Venkataraman Y, Fisher ZL, Gardner SM and Bartlett EL (2012) A computational model of inferior colliculus responses to amplitude modulated sounds in young and aged rats. Front. Neural Circuits 6:77. doi: 10.3389/fncir.2012.00077
Received: 29 April 2012; Accepted: 05 October 2012;
Published online: 02 November 2012.
Edited by:Eric D. Young, Johns Hopkins University, USA
Reviewed by:Paul B. Manis, University of North Carolina at Chapel Hill, USA
Copyright: © 2012 Rabang, Parthasarathy, Venkataraman, Fisher, Gardner and Bartlett. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Edward L. Bartlett, Weldon School of Biomedical Engineering, 206 South Martin Jischke Drive, West Lafayette, IN 47906, USA. e-mail: email@example.com
†Cal F. Rabang and Aravindakshan Parthasarathy have contributed equally to this work.