Investigating Disinhibitory Brain Mechanism in Tinnitus and Hearing Loss
Condition: Tinnitus; Hearing Loss
MeSH terms: Hearing Loss; Deafness; Tinnitus
Study type: Interventional

Summary: 
      Tinnitus, the perception of sound in the absence of an external acoustic stimulus. Tinnitus
      is often perceived inside the head rather than the ear and is a common condition with a
      prevalence estimated between 10 and 15% in adults. Between 1 and 3% of this population are
      having a significant impact on their quality of life. Despite its high prevalence, the
      underlying mechanisms of tinnitus still remain unclear.

      The majority of tinnitus cases associated with some degree of hearing loss, making hearing
      loss the biggest risk factor for tinnitus. Recently, it has been suggested that hearing
      deficits, such as speech-in-noise difficulty, can exist in the absence of any overt hearing
      loss within the audiometric range (0.125-8 kHz). This is referred to as "hidden hearing loss"
      and has been suggested to be associated with hearing loss at above-audiometric (> 8 kHz)
      frequencies.

      This project is aimed at studying the underlying mechanisms of tinnitus and the possible
      relation with overt or hidden hearing loss. Specifically, the investigators want to test the
      hypothesis that tinnitus is caused by maladaptive plasticity arising as a result of auditory
      input deprivation. This idea is supported by the finding that tinnitus may disappear when the
      hearing, and thus auditory input, recover. Disruptions at lower levels of the auditory
      pathway could lead to alterations in synaptic transmission and neurotransmitter release in
      more central regions of the auditory system (e.g., in the auditory cortex). This may create
      an imbalance between neuronal excitation and inhibition, and re-routing of auditory pathways,
      leading to abnormal neural excitability and connectivity.

      In this study, the investigators question whether auditory cortex disinhibition is
      specifically related to tinnitus, or is a consequence of hearing loss. To answer this
      question, the investigators propose to conduct a study that aims to investigate the
      inhibition mechanism by quantifying GABA concentration level, neural activity and functional
      connectivity strength of auditory cortex using non-invasive imaging techniques, namely
      Magnetic Resonance Spectroscopy (MRS) and functional Magnetic Resonance Imaging (fMRI). The
      investigators expected to possibly provide a tinnitus biomarker, and this may help to direct
      future treatments.
    

Detailed description: 
      SELECTION AND WITHDRAWAL OF PARTICIPANTS

      Recruitment

        1. Clinical routes Suitable candidates may be identified by the sites, at Ropewalk House
           Nottingham Audiology Services and ear, nose, and throat (ENT) services at Nottingham
           University Hospitals National Health Service (NHS) trust, via searches of their clinical
           databases or opportunistically during routine clinical appointments. Candidates will
           only be approached by a member of staff at the site or NIHR Clinical Research Network
           (CRN) staff to whom recruitment activities have been delegated by the local PI. All
           patient contact information will be kept confidential and undisclosed to the research
           team. The initial approach will be providing the participant with the information packs,
           that will contain (i) an invitation letter, (ii) a participant information sheet
           explaining all aspects pertaining to participation in the study and (iii) a reply slip.
           Potential participants who wish to find out more about the study will then be able to
           opt to be contacted by the researcher by completing a reply slip attached to the
           invitation letter and returning it in a pre-paid and addressed envelope. Alternatively,
           potential participants can contact the researcher directly via email and phone number
           that is written on the participant information sheet.

           It will be explained to the potential participant that entry into the trial is entirely
           voluntary and that their treatment and care will not be affected by their decision. It
           will also be explained that they can withdraw at any time, but attempts will be made to
           avoid this occurrence. In the event of their withdrawal, it will be explained that their
           data collected so far cannot be erased and the investigators will seek consent to use
           the data in the final analyses where appropriate.

           Posters about the study will be on display in the relevant clinical areas.

        2. Non-clinical routes:

           Non-clinical routes will include advertising the study via

             -  Invitation emails to NIHR Nottingham Hearing participant database. This database
                includes everyone that previously stating interest to takes part in tinnitus and
                hearing loss study (including healthy participants and hearing-related patients).

             -  Newsletter articles and announcements published by the relevant patient and
                professional organisations.

             -  Posts on social media channels (Twitter (@hearingnhir, @TIN_ACT @UoNPIBeacon) and
                Facebook.

           In all cases, fully informed consent will be sought by explaining the study's procedures
           and requirements following the standard script to interested potential participants. The
           potential participants will have ideally a minimum of 24 hours in which to decide
           whether or not to take part in this study. If the participant agrees to take part in the
           study, the consent form will be signed, during COVID-19 time this will be done
           electronically. In all cases, informed consent will be obtained and the consent form
           will have to be signed prior to any assessment or intervention.

           Expected duration of participant participation

           The study is expected to run between August 2021 until April 2022. The expected total
           duration of participation in the study from the time of informed consent is likely to
           range from one week to eight weeks. This prolonged time estimate is due to possible
           organisational difficulties in arranging the audiology assessment and the MRI scans,
           especially during the COVID-19 pandemic. There will be two visits for each participant,
           where each visit will last for around 1.5 hours.

           Removal of participants from therapy or assessments/Participant Withdrawal

           Participants may choose to withdraw from the study at any time without giving a reason.
           They will be withdrawn from the study if they are unable to be scanned (due to
           uncontrollable movement), or if they are unable for any reason to complete the audiology
           assessment. Participants will also be removed in the event of pregnancy, taking GABA
           enhancing or anti-depressants medication, having a cochlear or any metal implant that is
           not compatible with MRI scan, or having metal implant(s) during the time that they first
           agree to participate and the booked date for scanning, or withdrawal of consent.

           In the unique case relating to COVID-19, if participants report symptoms of the virus
           before the study appointment, it will be discussed if they still want to continue
           participating in the study, and while waiting for their 14 days quarantine the
           investigators will reschedule their appointment. However, in the case where participants
           are confirmed to have coronavirus before the study appointment, participants will be
           removed from the study.

           Participants will be made aware (via the information sheet and consent form) that should
           they withdraw the data collected to date cannot be erased and may still be used in the
           final analysis. If a participant withdraws from the study, the investigators will record
           the reason for and date of discontinuation. They will be replaced, such that at the end
           of the study, the number of completed scans, not the number of enrolled participants
           defines the end. Abrupt termination of enrolment in the study will not affect
           participant safety. The participants will be made aware that this will not affect their
           future care.

           STATISTICS

           Methods

           The investigators will use three tests to analyse the data: primary, secondary, and
           exploratory test.

           + Primary test

           Univariate group comparison between-group differences in imaging outcomes, this includes
           a comparison between:

           Auditory cortex GABA, GABA/Glx, and Cho level, Auditory cortex cerebral blood flow
           (CBF), Local functional connectivity density, Interhemispheric auditory cortices
           functional connectivity, Cross-modal functional connectivity between auditory and visual
           cortex, and Auditory cortex blood oxygen level-dependent (BOLD) response to visual
           attention task.

           Between-group test for differences in correlation, between:

           GABA and hearing loss, and Auditory cortex functional connectivity and hearing loss.

           + Secondary test: Within-group correlation analysis of imaging markers of inhibition
           (such as GABA, functional connectivity, CBF and BOLD response to attention) with
           audiometric results indexing sensory deafferentation. The investigators will also do
           regression analysis of imaging metrics with tinnitus severity.

           + Exploratory: Multivariate prediction model of tinnitus severity and regression of
           brain network metrics with affective tinnitus phenotypes.

           The findings will be evaluated by the investigator team. Due to the complex statistic
           question and strategy, the investigators will seek advice throughout the analysis from
           both experienced statistician and senior researcher. The analysis will take place on the
           University of Nottingham (UoN) computers, using R statistical software package and
           Matlab, and backed up to the UoN servers.

           Sample size and justification

           Approximately 60 subjects in total (30 per group). For details, please see below. All
           tests were done using the R statistical software package and STATA SE16.

           GABA

           Previous studies investigating GABA alteration in tinnitus and hearing loss patients are
           very limited, with the discrepancy between them. In Gao's study with a total sample of
           36 subjects, reported around 50% (r=-0.57) of total GABA variance is explained by
           hearing loss in the elderly cohort, with the assumption that half of their subjects have
           tinnitus (tin+) and the rest of the half did not have tinnitus (tin-), while in Sedley's
           study with a total sample of 28 subjects, reported significant GABA concentration
           reduced (median 1.12 vs 1.28 mM/L) in right auditory cortex for tin+ > tin-
           respectively.

           Using these values, the investigators can estimate their effect size using:

           Cohen's d = (M_1-M_2)/(SD pooled) Also, Cohen's d = 2r/√(1-r^2 )

           Where effect size for Gao and Sedley's study respectively are, r=-0.57 (correlation
           between hearing loss and GABA) and d=-3.7 (GABA effect size between patient and
           control). One might think of this as a promising effect, but the investigators are aware
           of the low power of these studies considering their small sample size compared to the
           population, and thus these effect sizes might be inflated and not represent the true
           effect size.

           The investigators then propose to recruit a bigger sample size, and with the time
           constraint and the limitation due to the COVID-19 pandemic, the realistic number of
           subjects that the investigators are pursuing is 30 per group (N total=60). With this
           sample size and based on knowledge from previous studies, the investigators estimated
           effect size of d=0.7 (two-sided test) and r=0.4 using 0.05 alpha value and 80% power.

           The investigators will also use a relative measurement to quantify GABA such as GABA/Cr
           ratio that presumably has a lower variance, and thus will power the effect size,
           compared to the absolute measure (i.e., mM/L).

           Previous pilot measurement has shown that GABA measurement was good enough in terms of
           repeatability and showing the right trend but failed to reach significance in
           within-subject measurement. Therefore, the other strategy is to involve and inter-relate
           the GABA measurement with other functional measures (resting-, visual task, tonotopy
           scan). The analysis will not be limited to only between-subject analysis, but the
           investigators will also do within-subject analysis that has shown to have more robust
           results.

           Functional connectivity

           In fMRI, the combination of a large number of dependent variables (i.e. huge number of
           voxel comparison) and a relatively small number of observations (subjects) resulted in
           underpowered studies with grossly inflated effect size and thus poorly represent the
           actual effects in the full sample/population. However, using meta-analysis, one can
           study whether reported findings from selected pooled studies (with a small sample) are
           really significant or not.

           Similar to the GABA approach, the investigators then estimate the effect size from a
           meta-analysis study of functional changes between tin + and tin - and compared it with
           the estimated effect size.

           r = z/√N Cohen's d = 2r/√(1-r^2 )

           The investigators estimate to be able to detect medium effect size, d=0.6 (N total= 30,
           whole brain, 0.05 alpha value, and 80% power).

           As the investigators are fully aware that the results might not represent the full
           picture of the true effect, the proposed study will still benefit tinnitus field
           research and add more power to validate previous findings. It is also noted that the
           meta-analysis study was using a whole-brain measurement (i.e. ReHo), where high variance
           is expected due to the big number of voxel comparison.

           Instead, the study proposes to focus on region-of-interest (ROIs) analysis to lower the
           variance, thus increasing the effect size. Defining the ROIs will be guided by an
           independent condition such as visual task and tonotopy scan, using Independent Component
           Analysis (ICA) analysis, and/or using anatomical maps such as Brodmann area. Some
           functional measures that will be applied are regional connectivity density,
           interregional correlations, and fractional amplitude of low-frequency fluctuations
           (fALFF). Cross-validation with GABA measurement, both between-subject and within-subject
           is expected to enrich the current knowledge between inhibition and neural activation
           changes in tinnitus patients.

           Procedures for missing, unused and spurious data

           In the case of missing or spurious data, the participants whose data is in question will
           be excluded from that particular analysis.
    

Intervention name(s): MRI scanning
Intervention type(s): Other
Intervention description(s): In the audiological assessment, participants will undergo various audiometric test, such as pure tone audiometry with extended high-frequency range, speech audiometry, tympanometry, and auditory reflex threshold. These tests are all noninvasive and aim to assess participants hearing threshold, speech-in-noise difficulty, whether or not they have conductive hearing loss, and test efferent auditory function. The appointment will take around 60-90 minutes. An experienced audiologist on-site will be in charge of this procedure.
In the MRI appointment, participant will undergo MRI scanning. Before the MRI scan, a researcher with experienced radiographer will re-check that the participant is safe to be scanned, with the standard University of Nottingham safety questionnaire. This rechecking step is necessary to make sure that participants are still eligible for the scanning. An experience radiographer will be in charge of this procedure.
Other intervention name(s): Audiological assessment
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Intervention model description: Cross sectional case-control multimodal MRI, audio- and psychometric study
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Tinnitus; Hearing loss; Inhibition; Functional connectivity; Structural connectivity