Neural networks of tinnitus in humans: Elucidating severity and habituation

The article reviews current data about the neural correlates of an individual's reaction to tinnitus, primarily from studies that employ magnetic resonance imaging (MRI). Human studies employing brain imaging remain the most commonly used method to understand neural biomarkers of the reaction to tinnitus, a subjective hearing disorder. Evidence from anatomical and functional MRI studies is reviewed to better understand the large-scale neural networks implicated in tinnitus habituation and severity. These networks are concerned with attention, audition, and emotion, both during tasks and at 'rest' when no goal-directed activity is expected. I place the data in the context of published literature and current theories about tinnitus severity, while explaining the challenges and limitations of human MRI studies. A possible model of habituation to tinnitus is described, that of the attention system (via the frontal cortex) suppressing the response from the amygdala and the use of alternate nodes of the limbic system such as the insula and the parahippocampal gyrus when mediating emotion.