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The Journal of Neuroscience, September 3, 2008, 28(36):8885-8896; doi:10.1523/JNEUROSCI.2693-08.2008

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Behavioral/Systems/Cognitive
Increasing Spectrotemporal Sound Density Reveals an Octave-Based Organization in Cat Primary Auditory Cortex

Arnaud J. Noreña,¹ Boris Gourévitch,² Martin Pienkowski,² Greg Shaw,² and Jos J. Eggermont^2,3

¹Integrative and Adaptive Neurobiology Laboratory, Unité Mixte de Recherche 6149, Université de Provence–Centre National de la Recherche Scientifique, Centre St Charles, 13331 Marseille Cedex 03, France, and Departments of ²Physiology and Biophysics and ³Psychology, University of Calgary, Calgary, Alberta, Canada T2N 1N4

Correspondence should be addressed to Dr. Jos J. Eggermont, Department of Psychology, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada ABT2N 1N4. Email: eggermon{at}ucalgary.ca

Auditory neurons are likely adapted to process complex stimuli, such as vocalizations, which contain spectrotemporal modulations. However, basic properties of auditory neurons are often derived from tone pips presented in isolation, which lack spectrotemporal modulations. In this context, it is unclear how to deduce the functional role of auditory neurons from their tone pip-derived tuning properties. In this study, spectrotemporal receptive fields (STRFs) were obtained from responses to multi-tone stimulus ensembles differing in their average spectrotemporal density (i.e., number of tone pips per second). STRFs for different stimulus densities were derived from multiple single-unit activity (MUA) and local field potentials (LFPs), simultaneously recorded in primary auditory cortex of cats. Consistent with earlier studies, we found that the spectral bandwidth was narrower for MUA compared with LFPs. Both neural firing rate and LFP amplitude were reduced when the density of the stimulus ensemble increased. Surprisingly, we found that increasing the spectrotemporal sound density revealed with increasing clarity an over-representation of response peaks at frequencies of 3, 5, 10, and 20 kHz, in both MUA- and LFP-derived STRFs. Although the decrease in spectral bandwidth and neural activity with increasing stimulus density can likely be accounted for by forward suppression, the mechanisms underlying the over-representation of the octave-spaced response peaks are unclear. Plausibly, the over-representation may be a functional correlate of the periodic pattern of corticocortical connections observed along the tonotopic axis of cat auditory cortex.

Key words: auditory cortex; local field potential; receptive field; multi-unit activity; stimulus density; electrode array

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Received June 10, 2008; accepted July 24, 2008.

Correspondence should be addressed to Dr. Jos J. Eggermont, Department of Psychology, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada ABT2N 1N4. Email: eggermon{at}ucalgary.ca

This article has been cited by other articles:

				B. Gourevitch, A. Norena, G. Shaw, and J. J. Eggermont Spectrotemporal Receptive Fields in Anesthetized Cat Primary Auditory Cortex Are Context Dependent Cereb Cortex, June 1, 2009; 19(6): 1448 - 1461. [Abstract] [Full Text] [PDF]

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