Henning Stracke

Listening to tailor-made notched music reduces tinnitus loudness and tinnitus-related auditory cortex activity

Maladaptive auditory cortex reorganization may contribute to the generation and maintenance of tinnitus. Because cortical organization can be modified by behavioral training, we attempted to reduce tinnitus loudness by exposing chronic tinnitus patients to self-chosen, enjoyable music, which was modified (“notched”) to contain no energy in the frequency range surrounding the individual tinnitus frequency. After 12 months of regular listening, the target patient group (n = 8) showed significantly reduced subjective tinnitus loudness and concomitantly exhibited reduced evoked activity in auditory cortex areas corresponding to the tinnitus frequency compared to patients who had received an analogous placebo notched music treatment (n = 8). These findings indicate that tinnitus loudness can be significantly diminished by an enjoyable, low-cost, custom-tailored notched music treatment, potentially via reversing maladaptive auditory cortex reorganization.

Attention Improves Population-Level Frequency Tuning in Human Auditory Cortex

Attention improves auditory performance in noisy environments by either enhancing the processing of task-relevant stimuli (“gain”), suppressing task-irrelevant information (“sharpening”), or both. In the present study, we investigated the effect of focused auditory attention on the population-level frequency tuning in human auditory cortex by means of magnetoencephalography. Using complex stimuli consisting of a test tone superimposed on different band-eliminated noises during active listening or distracted listening conditions, we observed that focused auditory attention caused not only gain, but also sharpening of frequency tuning in human auditory cortex as reflected by the N1m auditory evoked response. This combination of gain and sharpening in the auditory cortex may contribute to better auditory performance during focused auditory attention.

Frequency-specific modulation of population-level frequency tuning in human auditory cortex.

BackgroundUnder natural circumstances, attention plays an important role in extracting relevant auditory signals from simultaneously present, irrelevant noises. Excitatory and inhibitory neural activity, enhanced by attentional processes, seems to sharpen frequency tuning, contributing to improved auditory performance especially in noisy environments. In the present study, we investigated auditory magnetic fields in humans that were evoked by pure tones embedded in band-eliminated noises during two different stimulus sequencing conditions (constant vs. random) under auditory focused attention by means of magnetoencephalography (MEG).ResultsIn total, we used identical auditory stimuli between conditions, but presented them in a different order, thereby manipulating the neural processing and the auditory performance of the listeners. Constant stimulus sequencing blocks were characterized by the simultaneous presentation of pure tones of identical frequency with band-eliminated noises, whereas random sequencing blocks were characterized by the simultaneous presentation of pure tones of random frequencies and band-eliminated noises. We demonstrated that auditory evoked neural responses were larger in the constant sequencing compared to the random sequencing condition, particularly when the simultaneously presented noises contained narrow stop-bands.ConclusionThe present study confirmed that population-level frequency tuning in human auditory cortex can be sharpened in a frequency-specific manner. This frequency-specific sharpening may contribute to improved auditory performance during detection and processing of relevant sound inputs characterized by specific frequency distributions in noisy environments.

Hemispheric Asymmetry of Auditory Evoked Fields Elicited by Spectral versus Temporal Stimulus Change

The investigation of functional hemispheric asymmetries regarding auditory processing in the human brain still remains a challenge. Classical lesion and recent neuroimaging studies indicated that speech is dominantly processed in the left hemisphere, whereas music is dominantly processed in the right. However, recent studies demonstrated that the functional hemispheric asymmetries were not limited to the processing of highly cognitive sound signals like speech and music but rather originated from the basic neural processing of elementary sound features, that is, spectral and temporal acoustic features. Here, in contrast to previous studies, we used carefully composed tones and pulse trains as stimuli, balanced the overall physical sound input between spectral and temporal change conditions, and demonstrated the time course of neural activity evoked by spectral versus temporal sound input change by means of magnetoencephalography (MEG). These original findings support the hypothesis that spectral change is dominantly processed in the right hemisphere, whereas temporal change is dominantly processed in the left.

Sound processing hierarchy within human auditory cortex

Both attention and masking sounds can alter auditory neural processes and affect auditory signal perception. In the present study, we investigated the complex effects of auditory-focused attention and the signal-to-noise ratio of sound stimuli on three different auditory evoked field components (auditory steady-state response, N1m, and sustained field) by means of magnetoencephalography. The results indicate that the auditory steady-state response originating in primary auditory cortex reflects the signal-to-noise ratio of physical sound inputs (bottom–up process) rather than the listeners attentional state (top–down process), whereas the sustained field, originating in nonprimary auditory cortex, reflects the attentional state rather than the signal-to-noise ratio. The N1m was substantially influenced by both bottom–up and top–down neural processes. The differential sensitivity of the components to bottom–up and top–down neural processes, contingent on their level in the processing pathway, suggests a stream from bottom–up driven sensory neural processing to top–down driven auditory perception within human auditory cortex.

Left hemispheric dominance during auditory processing in a noisy environment

BackgroundIn daily life, we are exposed to different sound inputs simultaneously. During neural encoding in the auditory pathway, neural activities elicited by these different sounds interact with each other. In the present study, we investigated neural interactions elicited by masker and amplitude-modulated test stimulus in primary and non-primary human auditory cortex during ipsi-lateral and contra-lateral masking by means of magnetoencephalography (MEG).ResultsWe observed significant decrements of auditory evoked responses and a significant inter-hemispheric difference for the N1m response during both ipsi- and contra-lateral masking.ConclusionThe decrements of auditory evoked neural activities during simultaneous masking can be explained by neural interactions evoked by masker and test stimulus in peripheral and central auditory systems. The inter-hemispheric differences of N1m decrements during ipsi- and contra-lateral masking reflect a basic hemispheric specialization contributing to the processing of complex auditory stimuli such as speech signals in noisy environments.

Customized notched music training reduces tinnitus loudness

Chronic tinnitus is a symptom with high prevalence. There is evidence that the tinnitus perception is related to unfavorable cortical plastic changes. In our recent study we have developed and evaluated a customized music training strategy that appears capable of both reducing cortical tinnitus related neuronal activity and alleviating subjective tinnitus perception. We hypothesize that the regular and enjoyable music training reverses unprofitable cortical reorganization to a certain degree by means of the focused strengthening of auditory inhibitory neuronal networks.

Bottom-Up and Top-Down Driven Attentional Effects on Auditory Evoked Fields

Under natural environments, picking up relevant sound signals, which are embedded in other irrelevant sound signals, is an important ability for animals including humans. Bottom-up and top-down driven attention seems to play an important role in this process. In the present studies, we inves- tigated magnetic fields in humans that were evoked by pure tones embedded in band-eliminated noises during two different stimulus sequencing conditions (constant vs. random) and under two different auditory attentional conditions (focused vs. distracted) by means of magnetoencephalography. Constant stimulus sequencing was composed of identical pure tones overlaid with band-eliminated noises, whereas random sequencing was composed of pure tones of random frequencies overlaid with band-eliminated noises. We demon- strated that under focused auditory attention auditory evoked neural responses were sharper and larger in the constant se- quencing condition than the random sequencing condition. On the contrary, the auditory evoked fields under distracted audi- tory attention were larger, but not sharper in the constant sequencing condition compared to the random sequencing condition. Therefore, our results indicate that bottom-up driven audi- tory attention may mainly amplify excitatory neural networks, whereas the top-down auditory attention may both amplify and sharpen the neural activity via excitatory and inhibitory neural networks. The combination of bottom-up and top-down driven auditory attention would improve auditory performance in noisy environments.