Abstract
Acoustic therapy in tinnitus treatment is poorly characterized, and efficacy assessment depends on subjective descriptions. Narrow-band noise, notched sound, and white noise have positive therapeutic effects on monotonous tinnitus. Considering the tonotopic characteristics of the auditory system and the spectral characteristics of these three masking sounds, the activation pattern of the auditory cortex and the mechanism of inhibiting tinnitus may be different. This study aimed to compare the activation patterns of three spectrally different masking noises and study the correlation between the masking effects and variational amplitude of oxygenated hemoglobin (HbO) in the corresponding cortical regions. We also assessed near-infrared spectroscopy brain function imaging (NIRS) as an objective assessment tool in acoustic therapy. Patients with persistent non-pulsatile tinnitus and control volunteers without tinnitus were enrolled in this study. The subjects were seated in a sound-proof room, with two optode arrays covering the bilateral temporal lobe. Auditory stimuli were presented; stimulation sequences followed the block design: different noises appeared randomly and repeated in five cycles. Tinnitus match and residual inhibition were performed in the tinnitus group. The data analyses were conducted using the NIRS_SPM toolbox. The group analysis results showed that the narrow-band noise caused a marginally significant decrease in HbO signal in the Brodmann 21 region (BA21), while white noise caused a significant increase in HbO signal in BA21. Notched sound did not cause significant changes in the HbO signal in the temporal cortex. And none of the three masking noises caused significant changes in the HbR signal in the temporal cortex. The depth of residual inhibition induced by the narrow-band noise and white noise significantly correlated with ΔHbO in the region of interest (ROI). However, neither the depth nor duration of the residual inhibition induced by notched sound correlated with the ΔHbO. Thus, NIRS showed three cortical activation patterns induced by three different masking noises, and correlations between residual inhibition effects and change of HbO amplitude were found. NIRS could therefore be applied in objective assessment of acoustic therapy.
Highlights
Tinnitus is defined as phantom sound perception in the absence of an external sound source and is experienced by 10–15% of the general population (Sereda et al, 2018)
We used a crosssectional method to explore whether functional near-infrared spectroscopy technology could be used to detect different cortical activation characteristics of three representative masking sounds in the clinic and to determine whether the masking effect of different noises is related to the amplitude of ∆HbO in the corresponding cortical regions
Our results illustrate the potential of fNIRS technology in demonstrating the mechanism of different masking sounds and as an objective reference for clinical masking sound fitting
Summary
Tinnitus is defined as phantom sound perception in the absence of an external sound source and is experienced by 10–15% of the general population (Sereda et al, 2018). The spontaneous firing of neurons that occurs throughout the peripheral and central auditory nervous systems; even in the absence of sound in the environment, there is some level of nerve firing or spontaneous firing within the auditory nervous system (San Juan et al, 2017). Tonotopicity is maintained from the level of the basilar membrane of the cochlea to the central auditory structures and auditory cortex. Neural synchrony, or the balance of excitatory and inhibitory neural firing within the central auditory system, must be maintained to preserve the neural coding of auditory input (Noreña and Farley, 2013). Excitation and inhibition are important neural functions within the auditory pathway (Pickles, 2008). When transduction occurs within the inner ear, all fibers of the auditory nerve are excited, with no inhibition. Current theories of the origin of tinnitus-related to abnormalities in spontaneous firing rate, tonotopicity, and/or neural synchrony
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