Interval-counting neurons in the anuran auditory midbrain: factors underlying diversity of interval tuning |
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Authors: | Gary J Rose Christopher J Leary Christofer J Edwards |
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Institution: | (1) Department of Biology, University of Utah, 257 South 1400 East Rm 204, Salt Lake City, UT 84112, USA;(2) Present address: Department of Biology, University of Mississippi, Box 1848, Oxford, MS 38677, USA |
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Abstract: | In anurans, the temporal patterning of sound pulses is the primary information used for differentiating between spectrally
similar calls. One class of midbrain neurons, referred to as ‘interval-counting’ cells, appears to be particularly important
for discriminating among calls that differ in pulse repetition rate (PRR). These cells only respond after several pulses are
presented with appropriate interpulse intervals. Here we show that the range of selectivity and sharpness of interval tuning
vary considerably across neurons. Whole-cell recordings revealed that neurons showing temporally summating excitatory postsynaptic
potentials (EPSPs) with little or no inhibition or activity-dependent enhancement of excitation exhibited low-pass or band-pass
tuning to slow PRRs. Neurons that showed inhibition and rate-dependent enhancement of excitation, however, were band-pass
or high-pass to intermediate or fast PRRs. Surprisingly, across cells, interval tuning based on membrane depolarization and
spike rate measures were not significantly correlated. Neurons that lacked inhibition showed the greatest disparities between
these two measures of interval tuning. Cells that showed broad membrane potential-based tuning, for example, varied considerably
in their spike rate-based tuning; narrow spike rate-based tuning resulted from ‘thresholding’ processes, whereby only the
largest depolarizations triggered spikes. The potential constraints associated with generating interval tuning in this manner
are discussed. |
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