| Abstract #4101, Date Tuesday, Feb 22 2000 1:00PM - 12:00PM , Session , |
| Simulating the directional sensitivity of cochlear nucleus neurons to frequency-modulated stimuli |
| Yidao Cai , Edward Walsh , Joann Mcgee |
| Frequency-modulated (FM) stimuli are common in speech, especially in encoding formant transitions. Some neurons in the cochlear nucleus (CN) respond preferentially to FM sweeps in one direction and therefore may be associated with processing of formant transitions in speech. Fernald (1971) proposed that such a directional sensitivity can be accounted for by an orderly distribution of auditory nerve (AN) fiber inputs sorted according to fiber characteristic frequency (CF). However, a recent modeling study (Levy and Kipke, 1997) failed to produce asymmetric responses with orderly distributed inputs. In this study, we investigate this phenomenon using octopus cell models described previously (Cai et al. 1997, 1999). Inputs to the model were AN spike trains generated with a program adapted from that of Carney (1993). Subsets of the inputs, selected from CFs of 500-6000 Hz, were applied to the model in an orderly fashion, with the lowest-CF inputs contacting the soma. FM stimuli between 100 Hz and 10 kHz, were ramped in frequency either from low to high and returning to low, or from high to low and returning to high, and had sweep rates of 50-400 kHz/s. Models producing an On-I PSTH pattern exhibited a preference of low-to-high ramps and unidirectional responses, regardless of the starting frequency of the stimulus. The expression of such a preference and unidirectional responses was dependent upon sweep rate and stimulus level, similar to results observed experimentally (Britt and Starr, 1976). When fewer low-threshold K channels (KLT) were included in the model, weaker directional sensitivity was displayed. A stellate cell (chopper) model showed no preference to sweep direction. Reversing the order of the inputs (i.e. with highest-CF inputs contacting the soma) did not reverse the preference to sweep direction. These results suggest that, at least under the conditions we simulated, an orderly distribution of AN inputs is not critical to a neuron's directional sensitivity to FM sweeps. On the other hand, the same basic underlying mechanisms that produce the onset PSTH pattern (the KLT channel and the low input resistance) appear to be responsible. |
| Supported by NIDCD grant numbers DC01007 and DC00982. |
Citation for this abstract:
Cai, Y. E.J. Walsh and J. McGee (2000). Simulating the directional sensitivity of cochlear nucleus neurons to frequency-modulated stimuli Assoc. Res. Otolaryngol. Abstr.
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