title: The auditory midbrain of people with tinnitus: abnormal sound-evoked activity revisited.
abstract: Sound-evoked fMRI activation of the inferior colliculi (IC) was compared between tinnitus and non-tinnitus subjects matched in threshold (normal), age, depression, and anxiety. Subjects were stimulated with broadband sound in an "on/off" fMRI paradigm with and without on-going sound from the scanner coolant pump. (1) With pump sounds off, the tinnitus group showed greater stimulus-evoked activation of the IC than the non-tinnitus group, suggesting abnormal gain within the auditory pathway of tinnitus subjects. (2) Having pump sounds on reduced activation in the tinnitus, but not the non-tinnitus group. This result suggests response saturation in tinnitus subjects, possibly occurring because abnormal gain increased response amplitude to an upper limit. (3) In contrast to Melcher et al. (2000), the ratio of activation between right and left IC did not differ significantly between tinnitus and non-tinnitus subjects or in a manner dependent on tinnitus laterality. However, new data from subjects imaged previously by Melcher et al. suggest a possible tinnitus subgroup with abnormally asymmetric function of the IC. The present and previous data together suggest elevated responses to sound in the IC are common among those with tinnitus and normal thresholds, while abnormally asymmetric activation is not, even among those with lateralized tinnitus.
authors.affiliation: Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA. jennifer_melcher@meei.harvard.edu
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Melcher
authors.forename: Robert A
authors.initials: RA
authors.lastname: Levine
authors.forename: Christopher
authors.initials: C
authors.lastname: Bergevin
authors.forename: Barbara
authors.initials: B
authors.lastname: Norris
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D001301:Audiometry, Pure-Tone; D001306:Auditory Pathways / Q000473:pathology / Q000503:physiopathology*; D001309:Auditory Threshold; D001931:Brain Mapping / Q000379:methods; D016022:Case-Control Studies; D005072:Evoked Potentials, Auditory; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007245:Inferior Colliculi / Q000473:pathology / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009622:Noise / Q000009:adverse effects; D010470:Perceptual Masking; D013018:Sound Spectrography; D014012:Tinnitus / Q000473:pathology / Q000503:physiopathology*; D055815:Young Adult
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