Energy integration describes sound-intensity coding in an insect auditory system
Tim Gollisch, Hartmut Schütze, Jan Benda & Andreas V. M. Herz
Abstract
We investigate the transduction of sound stimuli into neural
responses and focus on locust auditory receptor cells. As in other
mechanosensory model systems, these neurons integrate acoustic
inputs over a fairly broad frequency range. To test three
alternative hypotheses about the nature of this spectral
integration (amplitude, energy, pressure), we perform
intracellular recordings while stimulating with superpositions of
pure tones. On the basis of online data analysis and automatic
feedback to the stimulus generator, we systematically explore
regions in stimulus space that lead to the same level of neural
activity. Focusing on such iso-firing-rate regions allows for a
rigorous quantitative comparison of the electrophysiological data
with predictions from the three hypotheses that is independent of
nonlinearities induced by the spike dynamics. We find that the
dependence of the firing rates of the receptors on the composition
of the frequency spectrum can be well described by an
energy-integrator model. This result holds at stimulus onset as
well as for the steady-state response, including the case in which
adaptation effects depend on the stimulus spectrum. Predictions of
the model for the responses to bandpass-filtered noise stimuli are
verified accurately. Together, our data suggest that the
sound-intensity coding of the receptors can be understood as a
three-step process, composed of a linear filter, a summation of
the energy contributions in the frequency domain, and a
firing-rate encoding of the resulting effective sound
intensity. These findings set quantitative constraints for future
biophysical models.
Last modified: Fri Nov 28 11:23:37 CET 2008