Dr. Mitch Day
Dr. Mitchell Day, Assistant Professor of Biological Sciences, co-authored an article on “Neural population encoding and decoding of sound source location across sound level in the rabbit inferior colliculus” in the Journal of Neurophysiology. (21 October 2015 Vol. no. , DOI: 10.1152/jn.00643.2015)
His co-author was Bertrand Delgutte.
Abstract: At lower levels of sensory processing, the representation of a stimulus feature in the response of a neural population can vary in complex ways across different stimulus intensities, potentially changing the amount of feature-relevant information in the response. How higher-level neural circuits could implement feature decoding computations that compensate for these intensity-dependent variations remains unclear. Here, we focused on neurons in the inferior colliculus (IC) of unanesthetized rabbits, whose firing rates are sensitive to both the azimuthal position of a sound source and its sound level. We found that the azimuth tuning curves of an IC neuron at different sound levels tend to be linear transformations of each other. These transformations could either increase or decrease the mutual information between source azimuth and spike count with increasing level for individual neurons, yet population azimuthal information remained constant across the absolute sound levels tested (35, 50 and 65 dB SPL), as inferred from the performance of a maximum-likelihood, neural population decoder. We harnessed evidence of level-dependent, linear transformations to reduce the number of free parameters in the creation of an accurate, cross-level population decoder of azimuth. Interestingly, this decoder predicts monotonic azimuth tuning curves, broadly sensitive to contralateral azimuths, in neurons at higher levels in the auditory pathway.
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