Lateralized tinnitus studied with functional magnetic resonance imaging: abnormal inferior colliculus activation.
Level 4 - case-series / case-control
Small case-control / cross-sectional neuroimaging study.
PubMed 10669517 · doi:10.1152/jn.2000.83.2.1058
What was done
Functional magnetic resonance imaging (fMRI) was used to evaluate sound-evoked neural activation (percent signal change) in the inferior colliculus (IC) during binaural and monaural masking noise stimulation. The study compared 4 subjects with lateralized tinnitus (isolated to one ear, with normal or near-normal audiograms) against 9 reference subjects (comprising non-tinnitus controls and non-lateralized tinnitus subjects).
What was found
Binaural noise elicited abnormally asymmetric IC activation in all 4 lateralized tinnitus subjects, whereas activation between the left and right IC did not differ significantly in the 9 reference subjects. Lateralized tinnitus subjects demonstrated abnormally low sound-evoked percent signal change specifically in the IC contralateral to the tinnitus percept, yielding a significantly higher asymmetry ratio (ipsilateral to contralateral signal change) relative to controls. Monaural noise similarly caused asymmetric activation. Specific numerical values, effect sizes, and variance measures were not reported in the abstract.
Why it matters
It demonstrates that fMRI can detect functional abnormalities in the midbrain auditory pathway corresponding to lateralized tinnitus perception, supporting models of altered baseline neural activity or saturation in the contralateral inferior colliculus.
Limits
The sample size is extremely small (4 cases and 9 controls). The abstract does not provide exact quantitative values or statistical test metrics. Restricting inclusion to subjects with normal or near-normal hearing limits generalizability to the wider tinnitus population with concurrent hearing loss.
Cited by
- supports People with tinnitus who have normal audiometric thresholds exhibit hyperactivity in auditory centers of the brain, specifically in the inferior colliculus.