Subjective tinnitus, temporomandibular joint dysfunction, and serotonin modulation of neural plasticity: causal or casual triad?

Tinnitus and temporomandibular joint dysfunction (TMJD) are among the most common complaints encountered by physicians. Though the relationship between tinnitus and TMJD has attracted great interest during the past several years, theories attempting to explain this association are still few and inconsistent. Conceivably, TMJD could irritate auricolo-temporal nerve (ATN), triggering a somatosensory pathway-induced disinhibition of dorsal cochlear nucleus (DCN) activity in the auditory pathway. In genetically-predisposed TMJD patients, signals from cronically stimulated DCNs activating specific cortical neuronal networks, could yield plastic neural changes resulting in tinnitus. Based on current evidence of serotoninergic modulation of neural activity and plasticity in sensory pathways, reduced serotoninergic tone could promote plastic changes underlying tinnitus through diminished filtering of incoming signals. Therefore, the early establishment of specific treatments aimed at improving TMJD and/or boosting serotoninergic activity may be required to prevent the creation of 'tinnitus memory circuits'.