HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 98/3/1451    most recent 01203.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Malone, B. J. Articles by Semple, M. N. Search for Related Content PubMed PubMed Citation Articles by Malone, B. J. Articles by Semple, M. N.

Dynamic Amplitude Coding in the Auditory Cortex of Awake Rhesus Macaques

Center for Neural Science, New York University, New York, New York

Submitted 14 November 2006; accepted in final form 3 July 2007

In many animals, the information most important for processing communication sounds, including speech, consists of temporal envelope cues below 20 Hz. Physiological studies, however, have typically emphasized the upper limits of modulation encoding. Responses to sinusoidal AM (SAM) are generally summarized by modulation transfer functions (MTFs), which emphasize tuning to modulation frequency rather than the representation of the instantaneous stimulus amplitude. Unfortunately, MTFs fail to capture important but nonlinear aspects of amplitude coding in the central auditory system. We focus on an alternative data representation, the modulation period histogram (MPH), which depicts the spike train folded on the modulation period of the SAM stimulus. At low modulation frequencies, the fluctuations of stimulus amplitude in decibels are robustly encoded by the cycle-by-cycle response dynamics evident in the MPH. We show that all of the parameters that define a SAM stimulus—carrier frequency, carrier level, modulation frequency, and modulation depth—are reflected in the shape of cortical MPHs. In many neurons that are nonmonotonically tuned for sound amplitude, the representation of modulation frequency is typically sacrificed to preserve the mapping between the instantaneous discharge rate and the instantaneous stimulus amplitude, resulting in two response modes per modulation cycle. This behavior, as well as the relatively poor tuning of cortical MTFs, suggests that auditory cortical neurons are not well suited for operating as a "modulation filterbank." Instead, our results suggest that <20 Hz, the processing of modulated signals is better described as envelope shape discrimination rather than modulation frequency extraction.

This article has been cited by other articles:

				L. Qin, J. Y. Wang, and Y. Sato Representations of Cat Meows and Human Vowels in the Primary Auditory Cortex of Awake Cats J Neurophysiol, May 1, 2008; 99(5): 2305 - 2319. [Abstract] [Full Text] [PDF]