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- K. Wimmer, K. J. Hildebrandt,
R. M. Hennig, and K. Obermayer. Adaptation and Selective Information
Transmission in the Cricket Auditory Neuron AN2.
.
PLoS Computational Biology, 4(9):e1000182, 2008.
(FTP PDF, 1246 kb)
Sensory systems adapt their neural code to changes in the sensory
environment, often on multiple time-scales. Here, we report a new form of
adaptation in a first order auditory interneuron (AN2) of crickets. We
characterize the response of the AN2 neuron to amplitude-modulated sound
stimuli, and find that adaptation shifts the stimulus-response curves towards
higher stimulus intensities, with a time constant of 1.5 seconds for
adaptation and recovery. The spike responses were thus reduced for
low-intensity sounds. We then address the question whether adaptation leads
to an improvement of the signal's representation and compare the experimental
results with the predictions of two competing hypotheses: infomax, which
predicts that information conveyed about the entire signal range should be
maximized, and selective coding, which predicts that ''foreground`` signals
should be enhanced while ''background`` signals should be selectively
suppressed. We test how adaptation changes the input-response curve when
presenting signals with two or three peaks in their amplitude distributions,
for which selective coding and infomax predict conflicting changes. By means
of Bayesian data analysis, we quantify the shifts of the measured response
curves and also find a slight reduction of their slopes. These decreases in
slopes are smaller, and the absolute response thresholds are higher than
predicted by infomax. Most remarkably, and in contrast to the infomax
principle, adaptation actually reduces the amount of encoded information when
considering the whole range of input signals. The response curve changes are
also not consistent with the selective coding hypothesis, because the amount
of information conveyed about the loudest part of the signal does not
increase as predicted but remains nearly constant. Less information is
transmitted about signals with lower intensity.
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