Abstract #19449, Date "Sunday, Feb 4 2001 1:00PM - 12:00PM "
Session "E13 Auditory Pathways, Brainstem III - Extracellular Response Patterns and Coding Mechanisms "
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| Processing pitch-related information by cochlear nucleus neurons: Results from experimental and computational studies |
| Yidao CAI |
| "Octopus cells, which show onset responses, extract pitch-related periodicity information in harmonic complexes. This ability is, however, restricted to higher intensity levels in On-I type because of the low steady-state responses at lower levels. Furthermore, both experimental and computational studies demonstrate that On-I neurons perform poorly when starting phases of the harmonic components in the stimuli are randomized (Evans and Zhao, 1998, Cai et al., 1998, 2000). Data were collected from ventral cochlear nucleus neurons of the gerbil using harmonic complex stimuli. Onset neurons generally encoded stimulus fundamental frequency (F0) with sharper peaks in interspike interval (ISI) histograms than other types of neurons.
While most chopper neurons encoded F0 with less sharply defined ISI peaks at lower levels, some of them, which are dominated by intrinsic chopping patterns, failed to encode F0 in stimuli. A number of On-L/PLN and chopper neurons encoded F0 in both zero- and random-phased harmonic stimuli. As stimulus level was increased, all neurons except for On-I type showed decreased ability to encode F0 in their ISI. Simulations were performed using octopus cell model (Cai et al. 2000) and spike trains recorded from auditory-nerve (AN) fibers as inputs. The original model (On-I) only encodes F0 at higher levels. As the conductance of a low-threshold K channel (KLT) was decreased, the model neuron encoded F0 over a wider intensity range, but with less sharply defined ISI peaks. Further reduction of KLT caused the model to encode F0 only at low levels. Because KLT is a major determinant of onset response, these results suggest that KLT is a key element underlying onset neurons' ability to process pitch-related periodicity information. When inputs were adjusted so that the model's tuning became narrower, encoding of F0 in random-phased complexes was improved.
Since many CN neurons show better synchrony to F0 than AN fibers do, it appears that interspike interval representation of pitch is being transformed from all-order statistics at the AN level to the first-order statistics at the CN level and beyond.
Work supported by the Deafness Research Foundation. |
Citation for this abstract:
Cai, Y. (2001). Processing pitch-related information by cochlear nucleus neurons: Results from experimental and computational studies. Assoc. Res. Otolaryngol. Abstr.
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