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We investigated potential markers of susceptibility to tinnitus in a group of normal hearing young pilots aged 25–35 years and with 8 ± 5 years of aircraft noise exposure. 316 pilots were interviewed about their tinnitus status and were tested for hearing thresholds (audiograms) and distortion products otoacoustic emissions (DPOAE-grams). There was no subject with permanent tinnitus. 23% reported having occasionally perceived tinnitus after flight missions and 77% reported never having experienced tinnitus after flight missions. General discomfort in the ears to noise was higher in the occasional tinnitus group (15 vs. 6%). The major finding was that difference of susceptibility to tinnitus in normal hearing subjects exposed to noise on a daily basis seemed to be clearly related to lower DPOAEs, bilaterally, in the 1500- to 2800-kHz range. However, no difference could be observed between groups on audiograms at the 2-kHz frequency range. This study provided evidence of outer hair cell dysfunctions in normal hearing subjects exposed to noise and susceptible to tinnitus. Hypersensitivity to noise and decreased DPOAEs in a non-noise-specific frequency range support the idea of another alteration mechanism than noise itself. This point was discussed in the light of recent publications.

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Middle ear sensory information has never been localized in the homunculus of the somatosensory cortex (S1). We investigated the somatosensory representation of the middle ear in 15 normal hearing subjects. We applied small air pressure variations to the tympanic membrane while performing a 3T fMRI study. Unilateral stimulations of the right ear triggered bilateral activations in the caudal part of the postcentral gyrus in Brodmann area 43 (BA 43) and in the auditory associative areas 42 (BA 42) and 22 (BA 22). BA 43 has been found to be involved in activities accompanying oral intake, and could be more largely involved in pressure activities in the oropharynx area. The tympanic membrane is indirectly related to the pharynx area through the action of tensor tympani, which is a Eustachian tube muscle. The Eustachian tube muscles have a role in pressure equalisation in the middle ear and also have a role in the pharyngeal phase of swallowing. Activation of BA 42 and BA 22 could reflect activations associated with the bilateral acoustic reflex triggered prior to selfvocalization to adjust air pressure in the oropharynx during speech. We propose that BA 43, 42 and 22 are the cortical areas associated with middle ear function. We did not find representation of tympanic membrane movements due to pressure in S1, but its representation in the postcentral gyrus in BA 43 seems to suggest that at least part of this area conveys pure somatosensory information. inserm-00638231, version 1 -4 Nov 2011Agnès JOB 3