The Journal of Neuroscience, August 15, 2001, 21(16):6377-6386
Physiological Correlates of Comodulation Masking Release in the
Mammalian Ventral Cochlear Nucleus
Daniel
Pressnitzer2,
Ray
Meddis3,
Roel
Delahaye3, and
Ian M.
Winter1
1 Centre for the Neural Basis of Hearing, The
Physiological Laboratory, Cambridge, CB2 3EG United Kingdom,
2 Institut de Recherche et Coordination
Acoustique/Musique-Centre National de la Recherche
Scientifique, Unité Mixte Recherche 9912, 75004 Paris, France,
and 3 Department of Psychology, University of Essex,
Colchester, CO4 3SQ United Kingdom
Comodulation masking release (CMR) enhances the detection of
signals embedded in wideband, amplitude-modulated maskers. At least
part of the CMR is attributable to across-frequency processing, however, the relative contribution of different stages in the auditory
system to across-frequency processing is unknown. We have measured the
responses of single units from one of the earliest stages in the
ascending auditory pathway, the ventral cochlear nucleus, where across
frequency processing may take place. A sinusoidally amplitude-modulated
tone at the best frequency of each unit was used as a masker. A
pure tone signal was added in the dips of the masker modulation
(reference condition). Flanking components (FCs) were then added at
frequencies remote from the unit best frequency. The FCs were pure
tones amplitude modulated either in phase (comodulated) or out of phase
(codeviant) with the on-frequency component. Psychophysically, this CMR
paradigm reduces within-channel cues while producing an advantage of
~10 dB for the comodulated condition in comparison with the reference
condition. Some of the recorded units showed responses consistent with
perceptual CMR. The addition of the comodulated FCs produced a strong
reduction in the response to the masker modulation, making the signal
more salient in the poststimulus time histograms. A decision statistic based on d' showed that threshold was reached at lower
signal levels for the comodulated condition than for reference or
codeviant conditions. The neurons that exhibited such a behavior were
mainly transient chopper or primary-like units. The results obtained from a subpopulation of transient chopper units are consistent with a
possible circuit in the cochlear nucleus consisting of a wideband
inhibitor contacting a narrowband cell. A computational model was used
to confirm the feasibility of such a circuit.
Key words:
chopper unit; onset unit; lateral inhibition; cochlear
nucleus; multipolar cell; wideband inhibitor
Copyright © 2001 Society for Neuroscience 0270-6474/01/21166377-10$05.00/0
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