The Difference Between Uni- and Bilateral Auditory Phantom Percept

Objective: Tinnitus can be considered an auditory phantom percept, in which patients hear an internal sound in the absence of any external sound source, mimicking tonal memory. Tinnitus however can be perceived exclusively uni- or bilaterally.

Methods: The neurophysiological differences were investigated between unilateral and bilateral tinnitus using LORETA source localized resting state EEG recordings.

Results: The difference between unilateral and bilateral tinnitus is reflected by high frequency activity (beta and gamma) in the superior prefrontal gurus, right parahippocampus, right angular gyrus and right auditory cortex. Unilateral tinnitus is characterized by contralateral beta2 in the superior prefrontal gyrus in comparison to bilateral tinnitus, but gamma in comparison to non-tinnitus subjects. Bilateral tinnitus has delta activity in the ventrolateral prefrontal cortex in comparison to unilateral tinnitus, and bilateral beta1 in comparison to non-tinnitus subjects. Bilateral tinnitus is also characterized by bilateral frontopolar beta1 activity.

Conclusions: Unilateral and bilateral tinnitus can be differentiated based on their resting state oscillation patterns: beta3 and gamma-band activity in the superior premotor cortex, parahippocampal area and angular gyrus seem to form the core of a spatial localization network involved in tinnitus.

Significance: These differences should be taken into account when evaluating functional neuroimaging data relating to tinnitus.