MaST: MEG and Brain Stimulation in Tinnitus

Tinnitus is the awareness of a sound in the ear or head without any outside source. It affects around 15% of people in the UK. About 20% of people with tinnitus experience symptoms that negatively affect their quality of life including sleep disturbances, difficulties with hearing and concentration, social isolation, anxiety, depression, irritation or stress. Most common clinical management strategies for tinnitus include education and advice combined with some form of sound therapy. The effects of these management options are, however, variable. Currently, the exact aetiology of tinnitus is unknown although maladaptive plasticity due to sensorineural hearing loss is thought to play a big role. Neuroimaging studies have pointed to over-activation or excessive spontaneous activity within the central auditory cortex. Furthermore, electrophysiological techniques have confirmed the frontal cortex's role in tinnitus through dysfunctional top-down modulation.

Transcranial direct current stimulation (tDCS) is a neurostimulation technique in which weak currents (1-2 mA's) are delivered to the brain, thereby depolarising or hyperpolarising neurons within the desired region of cortex. tDCS is a non-invasive and easy to apply tool, delivered by applying two surface electrode to a patients head. It has previously been used as a treatment for depression, stroke rehabilitation, and cognitive enhancement.

Some studies have indicated potential benefit of tDCS in tinnitus patients, but this has not yet been investigated within the UK. Neuromodulation therapies should deliver a permanent reduction in tinnitus percept by driving the neuroplastic changes necessary to interrupt abnormal levels of oscillatory cortical activity and restore typical levels of activity. This change in activity should alter or interrupt the tinnitus percept (reduce or extinguish) and this should be concomitant with a change in the level of self-reported tinnitus handicap. The currently ongoing Cochrane review of neuromodulation (desynchronisation) for tinnitus in adults found mixed evidence for the electrical stimulation therapies for tinnitus, including tDCS. However, the review also found that the most recent tDCS trials that have used greater numbers of treatment sessions found significant reductions in tinnitus symptom severity, anxiety, and depression. Authors concluded that these findings warrant further trials of tDCS. Research studies using electroencephalography (EEG) or magnetoencephalography (MEG) suggested changes in oscillatory activity in different frequency bands that might be associated with tinnitus, however a consistent picture has not yet emerged. Reduction of this abnormal activity might signify a reduction in the level or perceived severity of TI and could potentially be used as a valuable indicator of the course of TI treatment.

In this project specific changes in brain activity that happen during a new treatment approach for tinnitus - transcranial Direct Current Stimulation (tDCS)- will be investigated. This will help to determine how the treatment might work, whether specific brain activity may be a meaningful biological indicator or objective measure of tinnitus, and provide a reliable measure of treatment-related change; this has not yet been achieved in tinnitus research but is crucial.

Data collection session will involve the participant completing the Tinnitus Functional Index (TFI) and Demographics and Tinnitus History Questionnaire (D\&THQ), which will provide the investigators with information about their personal tinnitus history including subjective characteristics such as loudness. The D\&THQ consists of questions selected from the European School for Interdisciplinary Tinnitus Research Screening Questionnaire (ESIT-SQ). Participants will undergo a standard hearing test, which will inform the investigators of any hearing loss. The participant's head shape will be digitized to aid in the spatial localization of the MEG signal. The participant will then undergo 40 minutes of MEG scanning (10 minutes of resting state without tDCS, 20 minutes of resting state MEG with either active or sham tDCS, and then another 10 minutes of resting state MEG without tDCS. The first 10 minutes will serve as a baseline of resting state oscillatory brain activity. The concurrent tDCS and MEG recording will allow the investigators to observe changes in oscillatory brain activity during tDCS. The last 10 minutes of MEG recording will allow the investigators to see whether any changes in oscillatory activity persist after the stimulation ends. After the MEG recording has finished, the participant will undergo an anatomical MRI scan. This will allow the investigators to take the participants' individual brain morphology into account when analysing the source of the MEG signal.

Eligibility Criteria:
Inclusion Criteria:

1. Aged 18 years or over
2. Have subjective tinnitus
3. Able to read and understand English
4. Safe to undergo tDCS (according to tDCS Safety Questionnaire)
5. Safe to undergo MRI scanning (according to MRI Safety Screening Questionnaire)

Exclusion Criteria:

1. Aged under 18 years
2. No tinnitus
3. Not able to read and understand English
4. Not safe to undergo tDCS (according to tDCS Safety Questionnaire)
5. Not safe to undergo MRI scanning (according to MRI Safety Screening Questionnaire)