Functional Near-Infrared Spectroscopy as New and Innovative Neuroimaging Tool in Tinnitus?

Background: In recent years, human neuroimaging enhanced the understanding of neural mechanisms of tinnitus. However, each neuroimaging technique has specific limitations. Here, we provide first preliminary data in tinnitus from functional near-infrared spectroscopy (fNIRS) - an optical, not magnetic approach to measure blood oxygenation level dependent signals. fNIRS is a valid and reliable method with limited spatial resolution, but was shown to be capable to measure activity in auditory cortex. Materials and Methods: White noise was presented in an event-related (40 x 1.75s with 12-14s breaks) and blockwise (12 x 20s with 20s breaks) manner in 40 patients with tinnitus and 20 controls comparable for age and gender. The fNIRS probe-sets (2 x 22 channels) were placed over temporal areas. Results: Preliminary analyses indicate that tinnitus was associated with reduced auditory cortical oxygenation in both designs in contrast to controls. Conclusions: fNIRS is capable to add relevant information to sound evoked activity in auditory cortex. Future studies might be able to add more precise knowledge of auditory cortex activity with respect to the laterality and the character of the tinnitus percept. fNIRS might also be valuable in measuring brain areas which are challenging measureable by functional magnetic resonance imaging, i.e., orbitalfrontal cortex due to susceptibility artefacts.In addition, further research should concentrate on resting state measurements or on combined fNIRS-EEG measurements obliterating the limitations of both techniques