Altered cortical and subcortical connectivity due to infrasound administered near the hearing threshold – Evidence from fMRI

In the present study, the brain’s response towards near- and supra-threshold infrasound (IS) stimulation (sound frequency < 20 Hz) was investigated under resting-state fMRI conditions. The study involved two consecutive sessions. In the first session, 14 healthy participants underwent a hearing threshold—as well as a categorical loudness scaling measurement in which the individual loudness perception for IS was assessed across different sound pressure levels (SPL). In the second session, these participants underwent three resting-state acquisitions, one without auditory stimulation (no-tone), one with a monaurally presented 12-Hz IS tone (near-threshold) and one with a similar tone above the individual hearing threshold corresponding to a ‘medium loud’ hearing sensation (supra-threshold). Data analysis mainly focused on local connectivity measures by means of regional homogeneity (ReHo), but also involved independent component analysis (ICA) to investigate inter-regional connectivity. ReHo analysis revealed significantly higher local connectivity in right superior temporal gyrus (STG) adjacent to primary auditory cortex, in anterior cingulate cortex (ACC) and, when allowing smaller cluster sizes, also in the right amygdala (rAmyg) during the near-threshold, compared to both the supra-threshold and the no-tone condition. Additional independent component analysis (ICA) revealed large-scale changes of functional connectivity, reflected in a stronger activation of the right amygdala (rAmyg) in the opposite contrast (no-tone > near-threshold) as well as the right superior frontal gyrus (rSFG) during the near-threshold condition. In summary, this study is the first to demonstrate that infrasound near the hearing threshold may induce changes of neural activity across several brain regions, some of which are known to be involved in auditory processing, while others are regarded as keyplayers in emotional and autonomic control. These findings thus allow us to speculate on how continuous exposure to (sub-)liminal IS could exert a pathogenic influence on the organism, yet further (especially longitudinal) studies are required in order to substantialize these findings

Patient perspectives on the need for improved hearing rehabilitation: A qualitative survey study of German cochlear implant users

BackgroundThe electrical cochlear implant (eCI) partially restores hearing in individuals affected by profound hearing impairment (HI) or deafness. However, the limited resolution of sound frequency coding with eCIs limits hearing in daily situations such as group conversations. Current research promises future improvements in hearing restoration which may involve gene therapy and optical stimulation of the auditory nerve, using optogenetics. Prior to the potential clinical translation of these technologies, it is critical that patients are engaged in order to align future research agendas and technological advancements with their needs.MethodsHere, we performed a survey study with hearing impaired, using an eCI as a means of hearing rehabilitation. We distributed a questionnaire to 180 adult patients from the University Medical Center Göttingen’s Department of Otolaryngology who were actively using an eCI for 6 months or more during the time of the survey period. Questions revolved around patients needs, and willingness to accept hypothetical risks or drawbacks associated with an optical CI (oCI).ResultsEighty-one participants responded to the questionnaire; 68% were greater than 60 years of age and 26% had bilateral eCIs. Participants expressed a need for improving the performance beyond that experienced with their current eCI. Primarily, they desired improved speech comprehension in background noise, greater ability to appreciate music, and more natural sound impression. They expressed a willingness for engaging with new technologies for improved hearing restoration. Notably, participants were least concerned about hypothetically receiving a gene therapy necessary for the oCI implant; but expressed greater reluctance to hypothetically receiving an implant that had yet to be evaluated in a human clinical trial.ConclusionThis work provides a preliminary step in engaging patients in the development of a new technology that has the potential to address the limitations of electrical hearing rehabilitation

ReHo results.

<p>Statistical analysis of beta values extracted from the respective clusters observed in the whole-brain contrasts.</p

Results of the whole-brain analysis comparing regional homogeneity (ReHo) as derived from resting-state acquisitions during near-threshold vs. no-tone condition.

<p>Results of the whole-brain analysis comparing regional homogeneity (ReHo) as derived from resting-state acquisitions during near-threshold vs. no-tone condition.</p

Significant condition differences in resting state fMRI of the ICA.

<p>Significant condition differences in resting state fMRI of the ICA.</p

Acoustical characterization of 14 participants according to hearing threshold and categorical loudness scaling measurements for an IS-pure tone at 12 Hz.

<p>Acoustical characterization of 14 participants according to hearing threshold and categorical loudness scaling measurements for an IS-pure tone at 12 Hz.</p

Schematic drawing of the experimental setup.

<p>Schematic drawing of the experimental setup.</p

Results of whole-brain contrast regional homogeneity (ReHo) maps acquired during near-threshold vs. no-tone condition.

<p>Higher local connectivity in: (A) Right superior temporal gyrus (rSTG) in a sagittal (left), coronal (middle) and transversal (right) slice, as well as in (B) Anterior cingulate cortex (ACC) (p < 0.001, cluster-size corrected by means of Monte Carlo simulation, k > 22). (C) Higher local connectivity in right amygdala (rAmyg) when using a more lenient cluster threshold of k > 10.</p

Box plot showing regional homogeneity (ReHo) differences across conditions.

<p>Box plot showing regional homogeneity (ReHo) differences across conditions.</p