Article

Subcallosal brain structure: Correlation with hearing threshold at supra-clinical frequencies (> 8 kHz), but not with tinnitus

Dept. of Otology and Laryngology, Harvard Medical School, Boston MA, USA
Hearing research (Impact Factor: 2.97). 04/2012; 295. DOI: 10.1016/j.heares.2012.03.013
Source: PubMed

ABSTRACT

This study tested for differences in brain structure between tinnitus and control subjects, focusing on a subcallosal brain region where striking differences have been inconsistently found previously. Voxel-based morphometry (VBM) was used to compare structural MRIs of tinnitus subjects and non-tinnitus controls. Audiograms of all subjects were normal or near-normal at standard clinical frequencies (≤8 kHz). Mean threshold through 14 kHz, age, sex and handedness were matched between groups. There were no definitive differences between tinnitus and control groups in modulated or unmodulated maps of gray matter (GM) probability (i.e., GM volume and concentration, respectively). However, when the image data were tested for correlations with parameters that were either not measured or not matched between the tinnitus and control groups of previous studies, a notable correlation was found: Threshold at supra-clinical frequencies (above 8 kHz) was negatively correlated with modulated GM probability in ventral posterior cingulate cortex, dorsomedial prefrontal cortex, and a subcallosal region that included ventromedial prefrontal cortex and coincided with previously-reported differences between tinnitus and control subjects. The results suggest an explanation for the discrepant findings in subcallosal brain: threshold at supra-clinical frequencies may have differed systematically between tinnitus and control groups in some studies but not others. The observed correlation between (1) brain structure in regions engaged in cognitive and attentional processes and (2) hearing sensitivity at frequencies generally considered unnecessary for normal human auditory behavior is surprising and worthy of follow up.

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    • "Most such studies investigated sound-evoked activity. Interpretation of these data is difficult as associated comorbidities such as hearing loss and hyperacusis have to be considered (Gu et al., 2010; Melcher et al., 2013; Schecklmann et al., 2013). If a tinnitus-like sound is used for stimulation it is a challenge to exactly measure the pitch and volume of the tinnitus (Hoare et al., 2014). "
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    ABSTRACT: Chronic tinnitus is associated with neuroplastic changes in auditory and non-auditory cortical areas. About 10 years ago, repetitive transcranial magnetic stimulation (rTMS) of auditory and prefrontal cortex was introduced as potential treatment for tinnitus. The resulting changes in tinnitus loudness are interpreted in the context of rTMS induced activity changes (neuroplasticity). Here, we investigate the effect of single rTMS sessions on oscillatory power to probe the capacity of rTMS to interfere with tinnitus-specific cortical plasticity. We measured 20 patients with bilateral chronic tinnitus and 20 healthy controls comparable for age, sex, handedness, and hearing level with a 63-channel electroencephalography (EEG) system. Educational level, intelligence, depressivity and hyperacusis were controlled for by analysis of covariance. Different rTMS protocols were tested: Left and right temporal and left and right prefrontal cortices were each stimulated with 200 pulses at 1 Hz and with an intensity of 60% stimulator output. Stimulation of central parietal cortex with 6-fold reduced intensity (inverted passive-cooled coil) served as sham condition. Before and after each rTMS protocol 5 min of resting state EEG were recorded. The order of rTMS protocols was randomized over two sessions with 1 week interval in between. Analyses on electrode level showed that people with and without tinnitus differed in their response to left temporal and right frontal stimulation. In tinnitus patients left temporal rTMS decreased frontal theta and delta and increased beta2 power, whereas right frontal rTMS decreased right temporal beta3 and gamma power. No changes or increases were observed in the control group. Only non-systematic changes in tinnitus loudness were induced by single sessions of rTMS. This is the first study to show tinnitus-related alterations of neuroplasticity that were specific to stimulation site and oscillatory frequency. The observed effects can be interpreted within the thalamocortical dysrhythmia model assuming that slow waves represent processes of deafferentiation and that high frequencies might be indicators for tinnitus loudness. Moreover our findings confirm the role of the left temporal and the right frontal areas as relevant hubs in tinnitus related neuronal network. Our results underscore the value of combined TMS-EEG measurements for investigating disease related changes in neuroplasticity.
    Full-text · Article · Nov 2015 · Frontiers in Cellular Neuroscience
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    • "Less well-known, however, are other hearing-related 744 variables that are beginning to be studied using brain imaging studies. These include hyperacusis 745 (Gu et al., 2010), hidden cochlear damage (Schaette and McAlpine, 2011), and hearing loss at 746 higher frequencies (Melcher et al., 2013). 747 In order for brain imaging tools to be used as effective diagnostic and prognostic tools for 748 tinnitus, we need to better understand these sources of neural variance, relate them to indices of 749 severity, and possibly cluster them into well-defined subgroups within the larger tinnitus 750 population. "
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    ABSTRACT: The article reviews current data about the neural correlates of an individual's reaction to tinnitus, primarily from studies that employ magnetic resonance imaging (MRI). Human studies employing brain imaging remain the most commonly used method to understand neural biomarkers of the reaction to tinnitus, a subjective hearing disorder. Evidence from anatomical and functional MRI studies is reviewed to better understand the large-scale neural networks implicated in tinnitus habituation and severity. These networks are concerned with attention, audition, and emotion, both during tasks and at 'rest' when no goal-directed activity is expected. I place the data in the context of published literature and current theories about tinnitus severity, while explaining the challenges and limitations of human MRI studies. A possible model of habituation to tinnitus is described, that of the attention system (via the frontal cortex) suppressing the response from the amygdala and the use of alternate nodes of the limbic system such as the insula and the parahippocampal gyrus when mediating emotion.
    Full-text · Article · Sep 2015 · Hearing research
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    • "Hearing loss is typically comorbid with tinnitus suggesting the tinnitus percept is a direct consequence of maladaptive neuroplastic responses to hearing loss [3]. Current models of tinnitus generation therefore focus on the potential consequences of hearing loss on neuronal activity within the central auditory system [4]–[12], although neuronal structures or networks responsible for tinnitus that are independent of those for hearing loss are yet to be convincingly determined [13]–[16]. "
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    ABSTRACT: BackgroundPrevious studies of frequency discrimination training (FDT) for tinnitus used repetitive task-based training programmes relying on extrinsic factors to motivate participation. Studies reported limited improvement in tinnitus symptoms.PurposeTo evaluate FDT exploiting intrinsic motivations by integrating training with computer-gameplay.MethodsSixty participants were randomly assigned to train on either a conventional task-based training, or one of two interactive game-based training platforms over six weeks. Outcomes included assessment of motivation, tinnitus handicap, and performance on tests of attention.ResultsParticipants reported greater intrinsic motivation to train on the interactive game-based platforms, yet compliance of all three groups was similar (∼70%) and changes in self-reported tinnitus severity were not significant. There was no difference between groups in terms of change in tinnitus severity or performance on measures of attention.ConclusionFDT can be integrated within an intrinsically motivating game. Whilst this may improve participant experience, in this instance it did not translate to additional compliance or therapeutic benefit.Trial RegistrationClinicalTrials.gov NCT02095262
    Full-text · Article · Sep 2014 · PLoS ONE
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