Dynamic amplitude coding in the auditory cortex of awake rhesus macaques

Brian J. Malone, Brian H. Scott, Malcolm Semple

Research output: Contribution to journalArticle

Abstract

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.

Original languageEnglish (US)
Pages (from-to)1451-1474
Number of pages24
JournalJournal of Neurophysiology
Volume98
Issue number3
DOIs
StatePublished - Sep 2007

Fingerprint

Auditory Cortex
Macaca mulatta
Neurons
Phonetics
Cues
Communication
Transfer (Psychology)

ASJC Scopus subject areas

  • Physiology
  • Neuroscience(all)

Cite this

Dynamic amplitude coding in the auditory cortex of awake rhesus macaques. / Malone, Brian J.; Scott, Brian H.; Semple, Malcolm.

In: Journal of Neurophysiology, Vol. 98, No. 3, 09.2007, p. 1451-1474.

Research output: Contribution to journalArticle

Malone, Brian J. ; Scott, Brian H. ; Semple, Malcolm. / Dynamic amplitude coding in the auditory cortex of awake rhesus macaques. In: Journal of Neurophysiology. 2007 ; Vol. 98, No. 3. pp. 1451-1474.
@article{4962ef93845f49eaa9af9acd2e5e56fb,
title = "Dynamic amplitude coding in the auditory cortex of awake rhesus macaques",
abstract = "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.",
author = "Malone, {Brian J.} and Scott, {Brian H.} and Malcolm Semple",
year = "2007",
month = "9",
doi = "10.1152/jn.01203.2006",
language = "English (US)",
volume = "98",
pages = "1451--1474",
journal = "Journal of Neurophysiology",
issn = "0022-3077",
publisher = "American Physiological Society",
number = "3",

}

TY - JOUR

T1 - Dynamic amplitude coding in the auditory cortex of awake rhesus macaques

AU - Malone, Brian J.

AU - Scott, Brian H.

AU - Semple, Malcolm

PY - 2007/9

Y1 - 2007/9

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=34548756122&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=34548756122&partnerID=8YFLogxK

U2 - 10.1152/jn.01203.2006

DO - 10.1152/jn.01203.2006

M3 - Article

VL - 98

SP - 1451

EP - 1474

JO - Journal of Neurophysiology

JF - Journal of Neurophysiology

SN - 0022-3077

IS - 3

ER -