A COMPUTER-MODEL OF AMPLITUDE-MODULATION SENSITIVITY OF SINGLE UNITS IN THE INFERIOR COLLICULUS

A computer model is presented of a neural circuit that replicates ampl itude-modulation (AM) sensitivity of cells in the central nucleus of t he inferior colliculus (ICC). The ICC cell is modeled as a point neuro n whose input consists of spike trains from a number of simulated vent ral cochlear nucleus (VCN) chopper cells. Input to the VCN chopper cel ls is provided by simulated spike trains from a model of the auditory periphery [Hewitt et al., J. Acoust. Sec, Am. 91, 2096-2109 (1992)]. T he performance of the model at the output of the auditory nerve, the c ochlear nucleus and ICC simulations in response to amplitude-modulated stimuli is described. The results are presented in terms of both temp oral and rate modulation transfer functions (MTFs) and compared with d ata from physiological studies in the literature. Qualitative matches were obtained to the following main empirical findings: (a) Auditory n erve temporal-MTFs are low pass, (b) VCN chopper temporal-MTFs are low pass at low signal levels and bandpass at moderate and high signal le vels, (c) ICC unit temporal-MTFs are low pass at low signal levels and broadly tuned bandpass at moderate and high signal levels, and (d) IC C unit rate-MTFs are sharply tuned bandpass at low and moderate signal levels and flat at high levels. VCN and ICC units preferentially sens itive to different rates of modulation are presented. The model suppor ts the hypothesis that cells in the ICC decode temporal information in to a rate code [Langner and Schreiner, J. Neurophysiol. 60, 1799-1822 (1988)], and provides a candidate wiring diagram of how this may be ac hieved.