title: Dynamic Structure of Neural Variability in the Cortical Representation of Speech Sounds.
abstract: Accurate sensory discrimination is commonly believed to require precise representations in the nervous system; however, neural stimulus responses can be highly variable, even to identical stimuli. Recent studies suggest that cortical response variability decreases during stimulus processing, but the implications of such effects on stimulus discrimination are unclear. To address this, we examined electrocorticographic cortical field potential recordings from the human nonprimary auditory cortex (superior temporal gyrus) while subjects listened to speech syllables. Compared with a prestimulus baseline, activation variability decreased upon stimulus onset, similar to findings from microelectrode recordings in animal studies. We found that this decrease was simultaneous with encoding and spatially specific for those electrodes that most strongly discriminated speech sounds. We also found that variability was predominantly reduced in a correlated subspace across electrodes. We then compared signal and variability (noise) correlations and found that noise correlations reduce more for electrodes with strong signal correlations. Furthermore, we found that this decrease in variability is strongest in the high gamma band, which correlates with firing rate response. Together, these findings indicate that the structure of single-trial response variability is shaped to enhance discriminability despite non-stimulus-related noise.
  
  
  
  Cortical responses can be highly variable to auditory speech sounds. Despite this, sensory perception can be remarkably stable. Here, we recorded from the human superior temporal gyrus, a high-order auditory cortex, and studied the changes in the cortical representation of speech stimuli across multiple repetitions. We found that neural variability is reduced upon stimulus onset across electrodes that encode speech sounds.
authors.affiliation: Departments of Neurological Surgery and Physiology, University of California-San Francisco, San Francisco, California 94143-0112, Center for Integrative Neuroscience, University of California-San Francisco, San Francisco, California 94158, University of California-Berkeley and University of California-San Francisco Joint Program in Bioengineering, Berkeley, California 94720-3370.
authors.forename: Benjamin K
authors.identifier: 0000-0001-5725-6910
authors.initials: BK
authors.lastname: Dichter
authors.affiliation: Departments of Neurological Surgery and Physiology, University of California-San Francisco, San Francisco, California 94143-0112, Center for Integrative Neuroscience, University of California-San Francisco, San Francisco, California 94158, Center for Neural Engineering and Prosthesis, University of California-San Francisco and University of California-Berkeley, Berkeley, California 94720-3370, Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, and.
authors.forename: Kristofer E
authors.initials: KE
authors.lastname: Bouchard
authors.affiliation: Departments of Neurological Surgery and Physiology, University of California-San Francisco, San Francisco, California 94143-0112, Center for Integrative Neuroscience, University of California-San Francisco, San Francisco, California 94158, University of California-Berkeley and University of California-San Francisco Joint Program in Bioengineering, Berkeley, California 94720-3370, Center for Neural Engineering and Prosthesis, University of California-San Francisco and University of California-Berkeley, Berkeley, California 94720-3370, University of California-San Francisco Epilepsy Center, San Francisco, California 94143 edward.chang@ucsf.edu.
authors.forename: Edward F
authors.initials: EF
authors.lastname: Chang
mesh_terms: D000161:Acoustic Stimulation; D001931:Brain Mapping; D000069280:Electrocorticography; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005163:Factor Analysis, Statistical; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D017711:Nonlinear Dynamics; D013067:Speech Perception / Q000502:physiology*; D013702:Temporal Lobe / Q000502:physiology*; D013997:Time Factors
keywords: ECoG; encoding; noise correlations; speech; superior temporal gyrus; variability