Lateralized auditory spatial perception and the contralaterality of cortical processing as studied with functional magnetic resonance imaging and magnetoencephalography

Abstract

Functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were used to study the relationships between lateralized auditory perception in humans and the contralaterality of processing in auditory cortex. Subjects listened to rapidly presented streams of short FM-sweep tone bursts to detect infrequent, slightly deviant tone bursts. The stimulus streams consisted of either monaural stimuli to one ear or the other or binaural stimuli with brief interaural onset delays. The onset delay gives the binaural sounds a lateralized auditory perception and is thought to be a key component of how our brains localize sounds in space. For the monaural stimuli, fMRI revealed a clear contralaterality in auditory cortex, with a contralaterality index (contralateral activity divided by the sum of contralateral and ipsilateral activity) of 67%. In contrast, the fMRI activations from the laterally perceived binaural stimuli indicated little or no contralaterality (index of 51%). The MEG recordings from the same subjects performing the same task converged qualitatively with the fMRI data, confirming a clear monaural contralaterality, with no contralaterality for the laterally perceived binaurals. However, the MEG monaural contralaterality (55%) was less than the fMRI and decreased across the several hundred millisecond poststimulus time period, going from 57% in the M50 latency range (20-70 ms) to 53% in the M200 range (170-250 ms). These data sets provide both quantification of the degree of contralaterality in the auditory pathways and insight into the locus and mechanism of the lateralized perception of spatially lateralized sounds.

Joint Representation of Spatial and Phonetic Features in the Human Core Auditory Cortex

“…This ratio is similar to previously reported spatial tuning of auditory cortical neurons in mammals (Malhotra et al, 2004; Middlebrooks and Pettigrew, 1981; Rajan et al, 1990). Our findings, however, contrast with several neuroimaging studies in humans that report little to no contralateral bias (Woldorff et al, 1999; Zimmer et al, 2006). This discrepancy could be the result of bias-coding rather than place-coding of sound direction, which would not be easily detected in fMRI (Werner-Reiss and Groh, 2008).…”

Effects of Auditory Stimuli in the Horizontal Plane on Audiovisual Integration: An Event-Related Potential Study

“…Our results showed that the contralateral auditory cortex was activated when unimodal auditory stimuli were presented in the left or right locations; this finding is consistent with previous studies [45]. However, no significant integration was found when visual stimuli were centrally presented and auditory stimuli were presented in the left (90°) or right (90°) location.…”

Neural Correlates of Natural Human Echolocation in Early and Late Blind Echolocation Experts

“…For comparison, we also applied this analysis to the left and right auditory cortex. Previous fMRI research has shown a contralateral bias in auditory cortex for monoaural stimulation [16]–[18]. But to date, fMRI research has not been able to detect a contralateral bias with binaural stimulation, even though subjects may report hearing the sound source to be lateralized to the left or right, e.g.…”