Coding of interaural time differences in the DNLL of the mongolian gerbil
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1
Bernstein Center for Computational Neuroscience, Germany
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2
Ludwig-Maximilians-Universitaet, Germany
The difference in traveling time of a sound from its origin to the two ears is called the interaural time difference (ITD). ITDs are the main cue for low-frequency-sound localization. The frequency of the stimulus modulates the ITD sensitivity of the response rates of neurons in the brain stem. This modulation is generally characterized by two parameters: The characteristic phase (CP) and the characteristic delay (CD). The CD corresponds to a difference in the temporal delays from the ear to the respective coincidence detector neuron. The CP is an additional phase offset the nature of which is still under debate. The two above characteristic quantities hence describe the best ITD at which a neuron responds maximally via (best ITD)=CD+CP/f, in which f is the frequency of the pure tone stimulus. We recorded neuronal firing rates in the dorsal nucleus of the lateral lemniscus (DNLL) of the mongolian gerbil for pure tone stimuli with varying ITD and frequency. Intrestingly, we found that CPs and CDs were strongly negatively correlated. To understand the observed distribution of CPs and CDs among the recorded population, we have assessed the mutual information of firing rate and ITD in terms of these two parameters. Therefore we computed noise entropies from rate distributions fitted to the experiments.
Our results show that the information-optimal distribution of CPs and CDs exhibits a similar negative correlation as the one experimentally observed. Assuming similar rate statistics, we make hypotheses about how CDs and CPs should optimally be distributed for mammals with various head diameters. As expected, the mutual information increases with head diameter. Moreover, for increasing head diameter the two distinct subclusters of high mutual information (peakers and troughers) fuse into one.
Conference:
Bernstein Conference on Computational Neuroscience, Frankfurt am Main, Germany, 30 Sep - 2 Oct, 2009.
Presentation Type:
Oral Presentation
Topic:
Sensory processing
Citation:
Lüling
H,
Siveke
I,
Grothe
B and
Leibold
C
(2009). Coding of interaural time differences in the DNLL of the mongolian gerbil.
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference on Computational Neuroscience.
doi: 10.3389/conf.neuro.10.2009.14.155
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Received:
28 Aug 2009;
Published Online:
28 Aug 2009.
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Correspondence:
Hannes Lüling, Bernstein Center for Computational Neuroscience, Munich, Germany, lueling@bio.lmu.de