Tinnitus sensitization: Sensory and psychophysiological aspects of a new pathway of acquired centralization of chronic tinnitus

Objective: Acquired centralized tinnitus (ACT) is the most frequent form of chronic tinnitus. The proposed ACT sensitization (ACTS) assumes a peripheral initiation of tinnitus whereby sensitizing signals from the auditory system establish new neuronal connections in the brain. Consequently, permanent neurophysiological malfunction within the information-processing modules results. Successful treatment has to target these malfunctioning information processing. We present in this study the neurophysiological and psychophysiological aspects of a recently suggested neurophysiological model, which may explain the symptoms caused by central cognitive tinnitus sensitization. Although conditioned reflexes, as a causal agent of chronic tinnitus, respond to extinction procedures, sensitization may initiate a vicious circle of overexcitation of the auditory system, resisting extinction and habituation. Data Sources: We used the literature database as indicated under References covering English and German works. Study Selection: For the ACTS model we extracted neurophysiological hypotheses of the auditory stimulus processing and the neuronal connections of the central auditory system with other brain regions to explain the malfunctions of auditory information processing. The model does not assume information-processing changes specific for tinnitus but treats the processing of tinnitus signals comparable with the processing of other external stimuli. The model uses the extensive knowledge available on sensitization of perception and memory processes and highlights the similarities of tinnitus with central neuropathic pain. Data Extraction: Quality, validity, and comparability of the extracted data were evaluated by peer reviewing. Data Synthesis: Statistical techniques were not used. Conclusion: According to the tinnitus sensitization model, a tinnitus signal originates (as a type I-IV tinnitus) in the cochlea. In the brain, concerned with perception and cognition, the 1) conditioned associations, as postulated by the tinnitus model of Jastreboff, and the 2) unconditioned sensitized stimulus responses, as postulated in the present ACTS model, are actively connected with and attributed to the tinnitus signal. Attention to the tinnitus constitutes a typical undesired sensitized response. Some of the tinnitus-associated attributes may be called essential, unconditioned sensitization attributes. By a process called facilitation, the tinnitus' essential attributes are suggested to activate the tinnitus response. The result is an undesired increase in responsivity, such as an increase in attentional focus to the eliciting tinnitus stimulus. The mechanisms underlying sensitization are known as a specific nonassociative learning process producing a structural fixation of long-term facilitation at the synaptic level. This sensitization model may be important for the development of a sensitization-specific treatment if extinction procedures alone do not lead to satisfactory outcome. Inasmuch as this model considers sensitization as a nonassociative learning process based on cortical plasticity, it is reasonable to assume that this learning process can be altered by counteracting learning procedures. These counteracting learning procedures may consist of tinnitus-specific cognitive and behavioral procedures.