Differences in auditory mismatch negativity and global functional connectivity caused by interaural time differences

Abstract

Our ability to localize low-frequency sounds relies on interaural time differences (ITD), a sensitivity that is fundamental to our ability to pinpoint sound sources in azimuth and segregate competing sound sources across a wide range of situations. However, the neural representation of ITD has not been well characterized. This study aimed to elucidate distinctions in evoked cortical potentials and global functional connectivity during the unattended processing of sound localization on the horizontal plane, by recording and analyzing the auditory mismatch negativity (MMN) in adults, employing a deviant-standard oddball paradigm. A centrally-positioned sound source at the midline of the horizontal plane (ITD = 0 μs) served as the standard stimulus, while lateralized sounds with varying ITDs constituted the deviants. Results of MMN characteristics and the distribution of theta band power revealed a contralateral regulation mechanism of sound localization. To delve deeper into functional connectivity dynamics among different deviant stimulus groups, we computed the phase lag index within the theta band. Augmented functional connectivity was found between frontal electrode pairs when sound stimuli were directed towards the central compared to peripheral locations. In addition, assessments of global efficiency demonstrated that the peripheral sound stimuli revealed a higher global efficiency for peripheral sound stimuli. These observations suggest that smaller deviation from the center angle engages enhanced top-down attentional modulation to salient features. In summary, our results reinforced the contralateral regulatory mechanism governing sound source localization and illuminated the unique characteristics of theta band neural responses.