title: Modulation-frequency-specific adaptation in awake auditory cortex.
abstract: Amplitude modulations are fundamental features of natural signals, including human speech and nonhuman primate vocalizations. Because natural signals frequently occur in the context of other competing signals, we used a forward-masking paradigm to investigate how the modulation context of a prior signal affects cortical responses to subsequent modulated sounds. Psychophysical "modulation masking," in which the presentation of a modulated "masker" signal elevates the threshold for detecting the modulation of a subsequent stimulus, has been interpreted as evidence of a central modulation filterbank and modeled accordingly. Whether cortical modulation tuning is compatible with such models remains unknown. By recording responses to pairs of sinusoidally amplitude modulated (SAM) tones in the auditory cortex of awake squirrel monkeys, we show that the prior presentation of the SAM masker elicited persistent and tuned suppression of the firing rate to subsequent SAM signals. Population averages of these effects are compatible with adaptation in broadly tuned modulation channels. In contrast, modulation context had little effect on the synchrony of the cortical representation of the second SAM stimuli and the tuning of such effects did not match that observed for firing rate. Our results suggest that, although the temporal representation of modulated signals is more robust to changes in stimulus context than representations based on average firing rate, this representation is not fully exploited and psychophysical modulation masking more closely mirrors physiological rate suppression and that rate tuning for a given stimulus feature in a given neuron's signal pathway appears sufficient to engender context-sensitive cortical adaptation.
authors: Coleman Memorial Laboratory, Department of Otolaryngology-Head and Neck Surgery, University of California, San Francisco, California 94143, bjmalone724@gmail.com.
authors: Brian J
authors: BJ
authors: Malone
authors: Coleman Memorial Laboratory, Department of Otolaryngology-Head and Neck Surgery, University of California, San Francisco, California 94143.
authors: Ralph E
authors: RE
authors: Beitel
authors: Comprehensive Hearing Center, Department of Otolaryngology-Head and Neck Surgery, University Hospital Wuerzburg, 97080 Wuerzburg, Germany and.
authors: Maike
authors: M
authors: Vollmer
authors: Department of Psychiatry, Child and Adolescent Division, University of California Semel Institute for Neuroscience and Behavior, Los Angeles, California 90024.
authors: Marc A
authors: MA
authors: Heiser
authors: Coleman Memorial Laboratory, Center for Integrative Neuroscience, and Department of Otolaryngology-Head and Neck Surgery, University of California, San Francisco, California 94143.
authors: Christoph E
authors: CE
authors: Schreiner
mesh_terms: D000161:Acoustic Stimulation; D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D001303:Auditory Cortex / Q000166:cytology* / Q000502:physiology*; D001306:Auditory Pathways; D005260:Female; D016014:Linear Models; D009474:Neurons / Q000502:physiology*; D010470:Perceptual Masking / Q000502:physiology*; D011601:Psychophysics; D011930:Reaction Time; D012453:Saimiri; D013016:Sound; D014851:Wakefulness
keywords: auditory; context; monkey; primate; suppression; unanesthetized