A Unified Theory for the Development of Tinnitus and Hyperacusis Based on Associative Plasticity in the Dorsal Cochlear Nucleus

Background/Objectives: Tinnitus and hyperacusis can occur together or in isolation, with hyperacusis being asso-ciated with tinnitus much more frequently than vice versa. This striking correlation be-tween tinnitus and hyperacusis prevalence implicates that there might be a common origin such as a (hidden) hearing loss and possibly interrelated neural mechanisms of pathological development of those two conditions. Here, we propose such interrelated pathological mechanisms. Methods: This is a theoretical work based solely on considerations and published data. Results: We propose a model localized in the dorsal cochlear nucleus (DCN) of the brain-stem, that is based on classical mechanisms of Hebbian and associative plasticity known from classical conditioning. Specifically, our model proposes that hyperacusis results from synaptic enhancement of cochlear input to the DCN, whereas chronic tinnitus re-sults from synaptic enhancement of somatosensory input to the DCN. Specific conditions leading to one or the other condition are discussed. Conclusions: Our model predicts that hearing loss leads to chronic tinnitus, while noise exposure (which may also cause hearing loss) leads to hyperacusis. We would like to emphasize that our aim with the proposed model is not to provide a self-contained theo-retical construct, but to stimulate thought regarding possible pathological causes of tinni-tus and hyperacusis that have not yet been investigated. Individual assumptions that cannot yet be substantiated by existing literature are intended to provide impetus for fu-ture experimental studies.