Using functional magnetic resonance imaging to explore the representation of binaural cues in human auditory cortex

Functional magnetic resonance imaging (fMRI) was used to examine representations of interaural differences of level (ILD) and time (ITD) in human auditory cortex (AC). In one experiment, ILD of amplitude-modulated sounds varied parametrically across 12-s blocks, with a single image acquired at the end of each block (i.e., using a “sparse” imaging protocol). In another experiment, ILD or ITD varied parametrically across brief (1-s) presentations, and responses measured from continuosly-acquired images using an “event-related” paradigm. Whole-head echo-planar imaging (~3x3x3 mm resolution) was conducted at 3T (Philips Achieva), with sounds presented via insert earphones (Sensimetrics). Blood-oxygenation-level-dependent (BOLD) signals were analyzed on each individual's cortical surface using FSL, Freesurfer, and MATLAB. In this presentation, results will be discussed in terms of (1) the tuning of BOLD responses to ILD and ITD; (2) the relationship between tuning to ILD and tuning to monaural intensity; (3) ILD-related information as assessed using multi-voxel pattern analysis; (4) adaptation of the BOLD response as a function of trial-to-trial variation in binaural cues; and (5) whether the BOLD responses reflect physical versus perceptual (e.g., perceived location or loudness) aspects of auditory experience. [Supported by NSF DBI-0107567, NIH R03-DC009482-02S1, R01-DC011548, T32-DC005361]