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What Can fMRI Teach Us About the Neural Code?

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Front. Hum. Neurosci. | doi: 10.3389/fnhum.2018.00141

Converging Evidence from Electrocorticography and BOLD fMRI for a Sharp Functional Boundary in Superior Temporal Gyrus Related to Multisensory Speech Processing

  • 1Neurosurgery, Baylor College of Medicine, United States
  • 2Michael E. DeBakey VA Medical Center (VHA), United States

Although humans can understand speech using the auditory modality alone, in noisy environments visual speech information from the talker's mouth can rescue otherwise unintelligible auditory speech. To investigate the neural substrates of multisensory speech perception, we compared neural activity from the human superior temporal gyrus in two datasets. One dataset consisted of direct neural recordings (electrocorticography, ECoG) from surface electrodes implanted in epilepsy patients (this dataset has been previously published). The second dataset consisting of indirect measures of neural activity using blood oxygen level dependent functional magnetic resonance imaging (BOLD fMRI). Both ECoG and fMRI participants viewed the same clear and noisy audiovisual speech stimuli and performed the same speech recognition task. Both techniques demonstrated a sharp functional boundary in the STG, spatially coincident with an anatomical boundary defined by the posterior edge of Heschl's gyrus. Cortex on the anterior side of the boundary responded more strongly to clear audiovisual speech than to noisy audiovisual speech while cortex on the posterior side of the boundary did not. For both ECoG and fMRI measurements, the transition between the functionally distinct regions happened within 10 mm of anterior-to-posterior distance along the STG. We relate this boundary to the multisensory neural code underlying speech perception and propose that it represents an important functional division within the human speech perception network.

Keywords: multisensory, Speech Perception, Temporal Lobe, electrocorticography (ECoG), BOLD fMRI, audiovisual speech perception, multisensory integration, Speech in noise

Received: 05 Jan 2018; Accepted: 28 Mar 2018.

Edited by:

Cheryl Olman, University of Minnesota, United States

Reviewed by:

Arun Bokde, Trinity College, Dublin, Ireland
Julian Keil, Christian-Albrechts-Universität zu Kiel, Germany  

Copyright: © 2018 Özker, Yoshor and Beauchamp. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Michael S. Beauchamp, Baylor College of Medicine, Neurosurgery, 1 Baylor Plaza Suite S104, Houston, 1 Baylor Plaza Suite S104, Houston, 77030, TX, United States, Michael.Beauchamp@bcm.edu