Central tinnitus and lateral inhibition: an auditory brainstem model.

Central tinnitus is used herein either to designate a tinnitus that originates in the central auditory system, or to refer to a component of a peripherally generated tinnitus that is exaggerated by auditory brain mechanisms. Findings from several research areas contribute to this analysis of central tinnitus. The inferior colliculus, in particular, is significant because of the distribution of lateral inhibition in this nucleus and because of the possible change in inhibition that follows bearing loss. There is also a convergence of auditory and non-auditory functions at inferior colliculus. One non-auditory function, the initiation of aversive behavioral responses, may be demonstrated with electrical or chemical stimulation of auditory nuclei in the vicinity of the midbrain. With reduction of central inhibition through hearing loss or aging, tinnitus activity may gain easier access to those subsystems that produce aversive responses. A neural model, conceptually based in inferior colliculus, assumes a pattern of lateral inhibition that is influenced by the distribution of cochlear pathology. Of special importance are the abrupt changes across the tonotopically organized outputs from the cochlea that are reflected in behavioral measures as an 'audiometric edge'. The neural response properties that derive from this assumption are related to properties of central tinnitus.