The functional anatomy of gaze-evoked tinnitus and sustained lateral gaze.

OBJECTIVE

To identify neural sites associated with gaze-evoked tinnitus (GET), an unusual condition that may follow cerebellar-pontine angle surgery.

METHODS

The authors examined eight patients with GET and used PET to map the neural sites activated by lateral gaze in them and seven age- and sex-matched control subjects.

RESULTS

In patients with GET, tinnitus loudness and pitch increased with lateral gaze and, to a lesser extent, up and down gaze. Evidence for neural activity related to GET was seen in the auditory lateral pontine tegmentum or auditory cortex. GET-associated nystagmus appears to activate the cuneus and cerebellar vermis. These sites were found in addition to an extensive network that included frontal eye fields and other sites in frontal, parietal, and temporal cortex that were activated by lateral gaze in seven control subjects and the patients. The unilateral deafness in patients with GET was associated with expansion of auditory cortical areas responsive to tones delivered to the good ear. In addition to GET, unilateral deafness, end-gaze nystagmus, and facial nerve dysfunction were common.

CONCLUSIONS

Patients with GET have plastic changes in multiple neural systems that allow neural activity associated with eye movement, including those associated with the neural integrator, to stimulate the auditory system. Anomalous auditory activation is enhanced by the failure of cross-modal inhibition to suppress auditory cortical activity. The time course for the development of GET suggests that it may be due to multiple mechanisms.