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The Journal of Neuroscience, September 2, 2009, 29(35):10989-10994; doi:10.1523/JNEUROSCI.2744-09.2009

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Behavioral/Systems/Cognitive
GABAergic Excitation of Spider Mechanoreceptors Increases Information Capacity by Increasing Entropy Rather than Decreasing Jitter

Keram Pfeiffer and Andrew S. French

Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada

Correspondence should be addressed Andrew S. French, Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 1X5, Canada. Email: andrew.french{at}dal.ca

Neurotransmitter chemicals excite or inhibit a range of sensory afferents and sensory pathways. These changes in firing rate or static sensitivity can also be associated with changes in dynamic sensitivity or membrane noise and thus action potential timing. We measured action potential firing produced by random mechanical stimulation of spider mechanoreceptor neurons during long-duration excitation by the GABA_A agonist muscimol. Information capacity was estimated from signal-to-noise ratio by averaging responses to repeated identical stimulation sequences. Information capacity was also estimated from the coherence function between input and output signals. Entropy rate was estimated by a data compression algorithm and maximum entropy rate from the firing rate. Action potential timing variability, or jitter, was measured as normalized interspike interval distance. Muscimol increased firing rate, information capacity, and entropy rate, but jitter was unchanged. We compared these data with the effects of increasing firing rate by current injection. Our results indicate that the major increase in information capacity by neurotransmitter action arose from the increased entropy rate produced by increased firing rate, not from reduction in membrane noise and action potential jitter.

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Received June 11, 2009; revised July 18, 2009; accepted July 22, 2009.

Correspondence should be addressed Andrew S. French, Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 1X5, Canada. Email: andrew.french{at}dal.ca

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