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The Journal of Neuroscience, June 18, 2008, 28(25):6304-6308; doi:10.1523/JNEUROSCI.0961-08.2008

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Brief Communications
Invariance and Sensitivity to Intensity in Neural Discrimination of Natural Sounds

Cyrus P. Billimoria,^1,2 Benjamin J. Kraus,^1,2 Rajiv Narayan,^1,2 Ross K. Maddox,^1,2 and Kamal Sen^1,2

¹Hearing Research Center, Department of Biomedical Engineering, and ²Center for Biodynamics and Program in Mathematical and Computational Neuroscience, Boston University, Boston, Massachusetts 02215

Correspondence should be addressed to Kamal Sen, Hearing Research Center, Department of Biomedical Engineering, Center for Biodynamics, Program in Mathematical and Computational Neuroscience, Boston University, 44 Cummington Street, Boston, MA 02215. Email: kamalsen{at}bu.edu

Intensity variation poses a fundamental problem for sensory discrimination because changes in the response of sensory neurons as a result of stimulus identity, e.g., a change in the identity of the speaker uttering a word, can potentially be confused with changes resulting from stimulus intensity, for example, the loudness of the utterance. Here we report on the responses of neurons in field L, the primary auditory cortex homolog in songbirds, which allow for accurate discrimination of birdsongs that is invariant to intensity changes over a large range. Such neurons comprise a subset of a population that is highly diverse, in terms of both discrimination accuracy and intensity sensitivity. We find that the neurons with a high degree of invariance also display a high discrimination performance, and that the degree of invariance is significantly correlated with the reproducibility of spike timing on a short time scale and the temporal sparseness of spiking activity. Our results indicate that a temporally sparse spike timing-based code at a primary cortical stage can provide a substrate for intensity-invariant discrimination of natural sounds.

Key words: auditory cortex; speech; birdsong; recognition; field L; zebra finch

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Received July 11, 2007; revised May 13, 2008; accepted May 14, 2008.

Correspondence should be addressed to Kamal Sen, Hearing Research Center, Department of Biomedical Engineering, Center for Biodynamics, Program in Mathematical and Computational Neuroscience, Boston University, 44 Cummington Street, Boston, MA 02215. Email: kamalsen{at}bu.edu

This article has been cited by other articles:

				G. D. Grana, C. P. Billimoria, and K. Sen Analyzing Variability in Neural Responses to Complex Natural Sounds in the Awake Songbird J Neurophysiol, June 1, 2009; 101(6): 3147 - 3157. [Abstract] [Full Text] [PDF]

				E. Larson, C. P. Billimoria, and K. Sen A Biologically Plausible Computational Model for Auditory Object Recognition J Neurophysiol, January 1, 2009; 101(1): 323 - 331. [Abstract] [Full Text] [PDF]

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