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.