Cortical representation of tympanic membrane movements due to pressure variation: An fMRI study

Abstract

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

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“…This area has previously been implicated in conveying pure somatosensory information of an auditory nature (Job et al, 2011). Literature on the functional significance of BA 43 in SAD is lacking, but it seems reasonable to suggest that hyperactivity in this region in people with SAD may be associated with a state of hypervigilance, often in concurrence with anxiety states.…”

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“…The tympanic membrane contains mechanical proprioceptors that are sensitive to pressure, tension and stretch (Nagai [185] identifying Pacinian corpuscules). The middle ear tympanoossicular chain contains two muscles, the tensor tympani and the stapedius muscles, which contract to reduce the amount of motion in the presence of intense acoustic fields [186]. When applying small air pressure changes sufficient to cause small movements of the tympanum, Job et al [186] used fMRI to show that proprioreceptors in the tympanic membrane responded by generating brain activity in a limited region of Brodmann area 43 at the caudal edge of the somatosensory cortex.…”

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“…The response was bilateral in the caudal part of the postcentral gyrus in Brodmann area 43, which has been implicated in oral intake. 27 These studies extend the findings from histological studies to the in vivo state, opening up the opportunity to ascertain not only whether OM can be due to issues of innervation but also whether degradation of the peripheral nervous system affects hearing.…”