There is no effective treatment available for individuals unable to compensate for bilateral profound loss of vestibular sensation, which causes chronic disequilibrium and blurs vision by disrupting vestibulo-ocular reflexes that normally stabilize the eyes during head movement. Previous work suggests that a multichannel vestibular prosthesis can emulate normal semicircular canals by electrically stimulating vestibular nerve branches to encode head movements detected by mutually orthogonal gyroscopes affixed to the skull. Until now, that approach has been limited by current spread resulting in distortion of the vestibular nerve activation pattern and consequent inability to accurately encode head movements throughout the full 3-dimensional (3D) range normally transduced by the labyrinths. We report that the electrically evoked 3D angular vestibulo-ocular reflex exhibits vector superposition and linearity to a sufficient degree that a multichannel vestibular prosthesis incorporating a precompensatory 3D coordinate transformation to correct misalignment can accurately emulate semicircular canals for head rotations throughout the range of 3D axes normally transduced by a healthy labyrinth.

The tympanic membrane or eardrum of human ear transfers sound waves into mechanical vibration from the external ear canal into the middle ear and cochlea. Mechanical properties of the tympanic membrane (TM) play an important role in sound transmission through the ear. Although limited resources about linear elastic properties of the TM are available in literature, there is a lack of measurement or modeling of viscoelastic properties of the TM at low stress levels. In this study, the uniaxial tensile, stress relaxation, and failure tests were conducted on fresh human cadaver TM specimens to explore mechanical properties of the TM. The experimental results were analyzed using the hyperelastic Ogden model and digital image correlation method. The constitutive equation and non-linear elastic properties of the TM were presented by functions of the stress and strain at the stress range from 0 to 1 MPa. Viscoelastic properties of the TM were described by the stress relaxation function and hysteresis. The results show that the uniaxial tensile test with the aid of digital image correlation analysis is a reliable and useful approach for measuring mechanical properties of ear tissues. The data presented in this paper contribute to ear biomechanics in both experimental measurement and theoretical analysis of ear tissues.

Profound bilateral loss of vestibular hair cell function can cause chronically disabling loss of balance and inability to maintain stable vision during head and body movements. We have previously shown that chinchillas rendered bilaterally vestibular-deficient via intratympanic administration of the ototoxic antibiotic gentamicin regain a more nearly normal 3-dimensional vestibulo-ocular reflex (3D VOR) when head motion information sensed by a head-mounted multichannel vestibular prosthesis (MVP) is encoded via rate-modulated pulsatile stimulation of vestibular nerve branches. Despite significant improvement versus the unaided condition, animals still exhibited some 3D VOR misalignment (i.e., the 3D axis of eye movement responses did not precisely align with the axis of head rotation), presumably due to current spread between a given ampullary nerve’s stimulating electrode(s) and afferent fibers in nontargeted branches of the vestibular nerve. Assuming that effects of current spread depend on relative orientation and separation between nerve branches, anatomic differences between chinchilla and human labyrinths may limit the extent to which results in chinchillas accurately predict MVP performance in humans. In this report, we describe the MVP-evoked 3D VOR measured in alert rhesus monkeys, which have labyrinths that are larger than chinchillas and temporal bone anatomy more similar to humans. Electrodes were implanted in five monkeys treated with intratympanic gentamicin to bilaterally ablate vestibular hair cell mechanosensitivity. Eye movements mediated by the 3D VOR were recorded during passive sinusoidal (0.2–5 Hz, peak 50°/s) and acceleration-step (1000°/s2 to 150°/s) whole-body rotations in darkness about each semicircular canal axis. During constant 100 pulse/s stimulation (i.e., MVP powered ON but set to stimulate each ampullary nerve at a constant mean baseline rate not modulated by head motion), 3D VOR responses to head rotation exhibited profoundly low gain [(mean eye velocity amplitude)/(mean head velocity amplitude) < 0.1] and large misalignment between ideal and actual eye movements. In contrast, motion-modulated sinusoidal MVP stimuli elicited a 3D VOR with gain 0.4–0.7 and axis misalignment of 21–38°, and responses to high-acceleration transient head rotations exhibited gain and asymmetry closer to those of unilaterally gentamicin-treated animals (i.e., with one intact labyrinth) than to bilaterally gentamicin-treated animals without MVP stimulation. In comparison to responses observed under similar conditions in chinchillas, acute responses to MVP stimulation in rhesus macaque monkeys were slightly better aligned to the desired rotation axis. Responses during combined rotation and prosthetic stimulation were greater than when either stimulus was presented alone, suggesting that the central nervous system uses MVP input in the context of multisensory integration. Considering the similarity in temporal bone anatomy and VOR performance between rhesus monkeys and humans, these observations suggest ...

An otitis media with effusion model in human temporal bones with two laser vibrometers was created in this study. By measuring the displacement of the stapes from the medial side of the footplate, the transfer function of the middle ear, which is defined as the displacement transmission ratio (DTR) of the tympanic membrane to footplate, was derived under different middle ear pressure and fluid in the cavity with a correction factor for cochlear load. The results suggest that the DTR increases with increasing frequency up to 4k Hz when the middle ear pressure was changing from 0 to 20 or -20 cm H20 (e.g., +/-196 daPa) and fluid level was increasing from 0 to a full middle ear cavity. The positive and negative pressures show different effects on the DTR. The effect of fluid on DTR varies between three frequency ranges: f < 1k, between 1k and 4k, and f > 4k Hz. These findings show how the efficiency of the middle ear system for sound transmission changes during the presence of fluid in the cavity and variations of middle ear pressure.