Loudness Modulation Research Articles

Human caudate nucleus subdivisions in tinnitus modulation.

The object of this study was to define caudate nucleus locations responsive to intraoperative direct electrical stimulation for tinnitus loudness modulation and relate those locations to functional connectivity maps between caudate nucleus subdivisions and auditory cortex. Six awake study participants who underwent bilateral deep brain stimulation (DBS) electrode placement in the caudate nucleus as part of a phase I clinical trial were analyzed for tinnitus modulation in response to acute stimulation at 20 locations. Resting-state 3-T functional MRI (fMRI) was used to compare connectivity strength between centroids of tinnitus loudness-reducing or loudness-nonreducing caudate locations and the auditory cortex in the 6 DBS phase I trial participants and 14 other neuroimaging participants with a Tinnitus Functional Index > 50. Acute tinnitus loudness reduction was observed at 5 caudate locations, 4 positioned at the body and 1 at the head of the caudate nucleus in normalized Montreal Neurological Institute space. The remaining 15 electrical stimulation interrogations of the caudate head failed to reduce tinnitus loudness. Compared to the caudate head, the body subdivision had stronger functional connectivity to the auditory cortex on fMRI (p < 0.05). Acute tinnitus loudness reduction was more readily achieved by electrical stimulation of the caudate nucleus body. Compared to the caudate head, the caudate body has stronger functional connectivity to the auditory cortex. These first-in-human findings provide insight into the functional anatomy of caudate nucleus subdivisions and may inform future target selection in a basal ganglia-centric neuromodulation approach to treat medically refractory tinnitus.Clinical trial registration no.: NCT01988688 (clinicaltrials.gov).

Association of Concurrent fNIRS and EEG Signatures in Response to Auditory and Visual Stimuli.

Functional near-infrared spectroscopy (fNIRS) has been proven reliable for investigation of low-level visual processing in both infants and adults. Similar investigation of fundamental auditory processes with fNIRS, however, remains only partially complete. Here we employed a systematic three-level validation approach to investigate whether fNIRS could capture fundamental aspects of bottom-up acoustic processing. We performed a simultaneous fNIRS-EEG experiment with visual and auditory stimulation in 24 participants, which allowed the relationship between changes in neural activity and hemoglobin concentrations to be studied. In the first level, the fNIRS results showed a clear distinction between visual and auditory sensory modalities. Specifically, the results demonstrated area specificity, that is, maximal fNIRS responses in visual and auditory areas for the visual and auditory stimuli respectively, and stimulus selectivity, whereby the visual and auditory areas responded mainly toward their respective stimuli. In the second level, a stimulus-dependent modulation of the fNIRS signal was observed in the visual area, as well as a loudness modulation in the auditory area. Finally in the last level, we observed significant correlations between simultaneously-recorded visual evoked potentials and deoxygenated hemoglobin (DeoxyHb) concentration, and between late auditory evoked potentials and oxygenated hemoglobin (OxyHb) concentration. In sum, these results suggest good sensitivity of fNIRS to low-level sensory processing in both the visual and the auditory domain, and provide further evidence of the neurovascular coupling between hemoglobin concentration changes and non-invasive brain electrical activity.

P414: Involvement of different cortico-subcortical circuits in chronic tinnitus: an sLORETA-based study in normoacousic patients

LP28 - Figure 1. Results of inter-subject envelope correlation in a SSAEP paradigm: correlations. The unsupervised cSPoC method was applied to pairs of subjects with an objective to maximize a correlation between the spectral power (here the envelope was used) of corresponding neuronal activities related to an intensity modulated auditory steady state stimulus. In contrast, the supervised SPoC method was applied to each subject individually, with an objective to maximize a correlation between the power of neural activity and the intensity modulation of the auditory stimulus. (A) Cross-validated correlations between envelopes of sources extracted by SPoC/cSPoC and loudness modulation (stimulus intensity) for each subject, as well as average across subjects. (B) Pairwise envelope correlations for all subjects as obtained by SPoC and cSPoC, averaged across subject pairs. (C, D) Pairwise envelope correlations for all subjects as obtained by SPoC and cSPoC, respectively. Error bars indiacte SEM.

Deep Brain Stimulation in Area LC Controllably Triggers Auditory Phantom Percepts

Tinnitus is predominantly viewed as the consequence of dysfunctional hyperactivity, plastic change, or synchronized oscillations in the central auditory system. An alternative to the current auditory-centric view of auditory phantom perception is the basal ganglia-centric view. Recent electrical stimulation experiments in area LC, a locus of the caudate nucleus positioned at its anterior body, has shown loudness modulation of existing tinnitus percepts. To demonstrate that auditory phantoms are gated by the dorsal striatum. Electrical stimulation in area LC via a deep brain stimulation lead was performed in 6 interactive adult subjects (3 with and 3 without chronic tinnitus) undergoing surgery to treat movement disorders. Tinnitus loudness was rated on a 0 to 10 scale, sound quality was described, and localization was referenced to 1 or both ears. Short-term area LC stimulation triggered new phantom tones, clicks, and frequency modulated sounds in 5 subjects and altered sound quality of an existing tinnitus percept in 1 subject. The results of this study indicate that perceptual awareness of auditory phantoms is contingent on satisfying a permission condition controlled by the dorsal striatum. Potential auditory phantoms are not automatically gated to reach perceptual awareness. A phantom percept gate control model is proposed. Neuromodulation of area LC can trigger temporary gate dysfunction and reversibly release new phantoms for conscious awareness. Restoration of restrictive dorsal striatal gate function to treat problematic phantom percepts may be realized by adopting long-term area LC neuromodulation and choosing optimal stimulation parameters.

Modulation of loudness by environmental visual information

Loudness of sounds heard in outdoor settings is reportedly subject to visual influences, viz., the visibility of sound sources [D. E. Aylor and L. E. Marks, J. Acoust. Soc. Am. 59, 397–400 (1976)] and the visibility of vegetation [B. E. Mulligan et al., J. Acoust. Soc. Am. Suppl. 1 67, S22 (1980)]. The latter finding, however, was considered to be questionable due to the possibility of differential masking by ambient noise in the outdoor sites investigated. To assess this possibility, a second experiment was conducted at the original five sites with equalized ambient noise levels. As in the first experiment, observers estimated loudness magnitudes of 500 Hz tones presented through headphones. Evidence of masking was apparent at all sites, but loudness again was found to increase as a function of the proportion of visual vegetation. This finding does not appear to be attributable to differential masking. A third experiment conducted in the laboratory relied upon photographic projections of the same sites a...

SUPER- AND SUBLIMINAL BINAURAL BEATS.

Based upon the work of Lane (1925) and Lehnhardt (1961), the phenomenon of binaural beats was further studied. The behaviour of the beats as a function of frequency points to three distinctly different frequency regions with an optimum audibility in the range from 90 to 800 cps, less clear from 850 to 1100 cps, audibility falling rapidly beyond 1100 to 1400 cps, disappearance at 1500 cps. In the optimum range the loudness modulation of binaural beats is comparable to that of a monaural, about 2 db modulated tone. Binaural beats are detectable at levels of 20 db below threshold in one ear, if the level in the other ear is above or near threshold.