Evidence of a functional reorganization in the auditory dorsal stream following unilateral hearing loss

Abstract

Unilateral hearing loss (UHL) generates a disruption of binaural hearing mechanisms, which impairs sound localization and speech understanding in noisy environments. We conducted an original study using fMRI and psychoacoustic assessments to investigate the relationships between the extent of cortical reorganization across the auditory areas for UHL patients, the severity of unilateral hearing loss, and the deficit in binaural abilities. Twenty-eight volunteers (14 UHL patients) were recruited (twenty-two females and six males). The brain imaging analysis demonstrated that UHL induces a shift in aural dominance favoring the better ear, with a cortical reorganization located in the non-primary auditory areas, ipsilateral (same side) to the better ear. This reorganization is correlated not only to the hearing loss severity but also to spatial localization abilities. A regression analysis between brain activity and patient's performance clearly showed that the spatial hearing deficit was linked to a functional alteration of the posterior auditory areas known to process spatial hearing. Altogether, our study reveals that UHL alters the dorsal auditory stream, which is deleterious to spatial hearing.

Proficiency in Using Level Cue for Sound Localization Is Related to the Auditory Cortical Structure in Patients With Single-Sided Deafness

“…However, findings are scarce regarding how the observed neuroplasticity in asymmetric hearing is related to binaural auditory performance, such as sound localization ability. In one recent fMRI study of subjects with varying degrees of asymmetric hearing loss ( Vannson et al, 2020 ), changes in auditory localization ability were associated with neural plasticity in the posterior auditory cortex, where structural correlation with localization performance was also observed in this study. Neuroimaging studies with sound localization tasks have not yet been reported, and neuroplasticity related to auditory spatial performance changes should be further elucidated with consideration of clinical variables such as the degree, duration, and onset of hearing asymmetry.…”

“…However, findings are scarce regarding how the observed neuroplasticity in asymmetric hearing is related to binaural auditory performance, such as sound localization ability. In one recent fMRI study of subjects with varying degrees of asymmetric hearing loss (Vannson et al, 2020), changes in auditory localization ability were associated with neural plasticity in the posterior auditory cortex, where structural correlation with localization performance was also observed in this study.…”

Ear-Specific Hemispheric Asymmetry in Unilateral Deafness Revealed by Auditory Cortical Activity

“…Using the mismatch negativity evoked by infrequent changes in sound location, Sonnadara et al (2006) found a longer latency in the positive peak in response to a large angle (90 • ) compared to a smaller one; they also alluded that this can be partially interpreted by applying the spatial channel theory suggested by Boehnke and Phillips (1999) who posited that 0 and 30 • are processed in the same spatial channel whereas 0 and 90 • (angles larger than 30 • ) are not. Moreover, according to the theory, spatial location information belonging to different channels is not processed in the lower level of the auditory system but rather in the higher order auditory cortex (Vannson et al, 2020). In this sense, the prolonged latency at the greater azimuth angles could be associated with the precise spatial processing properties of the central auditory system for between-channel discrimination.…”

“…For example, the findings from a recent study show a significant inverse relationship between speech perception ability, the duration of deafness, and cortical N1 responses in right-sided unilateral deafness, indicating that substantial neural plasticity occurs due to deafness in the right ear (Cañete et al, 2019). Similarly, a recent fMRI study also showed that a stronger dominance shift to the hemisphere ipsilateral to the better ear is significantly related to poorer horizontal sound localization in people with unilateral hearing loss (Vannson et al, 2020). Thus, the primary goal of this study is to determine whether electrophysiology can predict the behavioral perceptual ability of sound localization in UD adults.…”

Auditory cortex activation is modulated nonlinearly by stimulation duration: A functional near-infrared spectroscopy (fNIRS) study

“…In addition, the intensity was equalized according to the root mean square level. The vocal and nonvocal stimuli used in this study originated from the database exploited in previously published studies (Belin et al, 2000; Massida et al, 2011; Vannson et al, 2020). They comprised speech stimuli and nonspeech vocal stimuli (e.g., laughs, coughs) and environmental sounds, including sound alarms, car horns, streaming water, animal vocalizations, etc.…”