At frequencies above 3 kHz, the tympanic membrane vibrates chaotically. By having many resonances, the eardrum can transmit the broadest possible bandwidth of sound with optimal sensitivity. In essence, the eardrum works best through discord. The eardrum's success as an instrument of hearing can be directly explained through a combination of its shape, angular placement, and composition. The eardrum has a conical asymmetrical shape, lies at a steep angle with respect to the ear canal, and has organized radial and circumferential collagen fiber layers that provide the scaffolding. Understanding the role of each feature in hearing transduction will help direct future surgical reconstructions, lead to improved microphone and loudspeaker designs, and provide a basis for understanding the different tympanic membrane structures across species. To analyze the significance of each anatomical feature, a computer simulation of the ear canal, eardrum, and ossicles was developed. It is shown that a cone-shaped eardrum can transfer more force to the ossicles than a flat eardrum, especially at high frequencies. The tilted eardrum within the ear canal allows it to have a larger area for the same canal size, which increases sound transmission to the cochlea. The asymmetric eardrum with collagen fibers achieves optimal transmission at high frequencies by creating a multitude of deliberately mistuned resonances. The resonances are summed at the malleus attachment to produce a smooth transfer of pressure across all frequencies. In each case, the peculiar properties of the eardrum are directly responsible for the optimal sensitivity of this discordant drum.collagen fibers ͉ hearing sensitivity ͉ middle ear ͉ transducers T he function of the middle ear in terrestrial mammals is to transfer acoustic energy between the air of the ear canal to the fluid of the inner ear. The first and crucial step of the transduction process takes place at the tympanic membrane, which converts sound pressure in the ear canal into vibrations of the middle ear bones. Understanding how the tympanic membrane manages this task so successfully over such a broad range of frequencies has been a subject of research since Helmholtz's publication in 1868 (1, 2).Even though the function of the eardrum is clear and the anatomy of the eardrum is well characterized, the connection between the anatomical features and the ability of the eardrum to transduce sound has been missing. The missing structurefunction relationships can be summarized by the following three questions. Why does the mammalian eardrum have its distinctive conical and toroidal shape? What is the advantage of its angular placement in the ear canal? What is the significance of its highly organized radial and circumferential fibers?The shape of the human and feline eardrum is known from detailed Moiré interferometry contour maps (refs. 3 and 4 and Fig. 1a). From the contour maps, three-dimensional reconstructions reveal the striking similarity of the two eardrums. In both cases, the eardrum has an ell...

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Emerging evidence suggests that cocaine and other drugs of abuse can interfere with many aspects of cognitive functioning. The authors examined the effects of 0.1 -15 mg/kg of cocaine on Pavlovian contextual and cued fear conditioning in mice. As expected, pre-training cocaine dose-dependently produced hyperactivity and disrupted freezing. Surprisingly, when the mice were tested off-drug later, the group pre-treated with a moderate dose of cocaine (15 mg/kg) displayed significantly less contextual and cued memory, compared to saline control animals. Conversely, mice pre-treated with a very low dose of cocaine (0.1 mg/kg) showed significantly enhanced fear memory for both context and tone, compared to controls. These results were not due to cocaine's anesthetic effects, as shock reactivity was unaffected by cocaine. The data suggest that despite cocaine's reputation as a performance-enhancing and anxiogenic drug, this effect is seen only at very low doses, whereas a moderate dose disrupts hippocampus and amygdala-dependent fear conditioning. KeywordsHippocampus; Amygdala; Freezing; Memory A growing body of evidence supports the view that drugs of abuse interfere with many aspects of cognitive functioning. For example, cocaine use has been linked to deficits in such cognitive areas as attention, cognitive flexibility, and short-term and working memory [34,43]. However, these findings in humans are controversial as cocaine use is naturally confounded with many other variables [e.g. 23, 27, 31]. Some studies, in fact, provide evidence for enhancement of certain cognitive abilities in cocaine users [e.g. 27, 50]. Relatively few studies in animals have examined the effects of cocaine on learning outside of the realm of addiction (e.g. selfadministration, place preference, sensitization). Indeed, several studies have focused on the mechanisms underlying addiction, including structural plasticity [see 41 for review], but few have examined the acute, behavioral effects of cocaine in rodents on simple learning and memory paradigms. We believe that most researchers implicitly assume, as we once did, that cocaine, as a psychostimulant, would naturally enhance learning and memory. However, evidence now exists linking cocaine use with specific cognitive deficits [5,25,34,43] as well as with general problems such as unemployment [35]. Moreover, a view has emerged that addictive drugs such as cocaine may work by taking control of critical reinforcement-related learning and memory circuits in the brain [28]. If cocaine modulates such circuits, then it may 1 Address correspondence and reprint requests to: Suzanne C. Wood,

Objective To assess the safety, stability, and performance of the broad spectrum, light based Contact Hearing Device (CHD) on listeners with hearing impairment. Study Design Feasibility study. Setting Single-Site Research and Development Facility. Subjects Thirteen subjects with symmetric mild to severe sensorineural hearing impairment had the CHD placed bilaterally. Intervention A custom-molded light activated Tympanic Contact Actuator (TCA) was placed into each ear by a physician, where it stayed in contact with the umbo and a portion of the medial wall of the ear canal for four months. Each CHD was calibrated and programmed to provide appropriate broad-spectrum amplification. Main Outcome Measures Safety was determined through routine otologic examinations. Aided and pre-TCA-insertion unaided audiometric thresholds, Reception Threshold for Sentences (RTS), and Abbreviated Profile of Hearing Aid Benefit (APHAB) measurements were made to characterize system performance as well as the benefits of amplification via the CHD. Results The TCAs remained on subjects’ ears for an average total of 122 days, without causing signs of inflammation or infection, and there were no serious device-related adverse events. Measured average maximum output of 90–110 dB SPL in the 0.25–10 kHz range, average maximum gain before feedback of 40 dB, and functional gain through 10 kHz show extended bandwidth broad spectrum output and gain. RTS results showed significant aided improvements of up to 2.8 dB, and APHAB results showed clinically significant aided benefits in 11/12 (92%) subjects. Conclusion The safety, stability, and performance demonstrated in this initial 4-month study suggest that the CHD may offer a feasible way of providing broad-spectrum amplification appropriate to treat listeners with mild to severe hearing impairment.

The hypothesis is tested that an open-canal hearing device, with a microphone in the ear canal, can be designed to provide amplification over a wide bandwidth and without acoustic feedback. In the design under consideration, a transducer consisting of a thin silicone platform with an embedded magnet is placed directly on the tympanic membrane. Sound picked up by a microphone in the ear canal, including sound-localization cues thought to be useful for speech perception in noisy environments, is processed and amplified, and then used to drive a coil near the tympanic-membrane transducer. The perception of sound results from the vibration of the transducer in response the electromagnetic field produced by the coil. Sixteen subjects (ranging from normal-hearing to moderately hearing-impaired) wore this transducer for up to a ten-month period, and were monitored for any adverse reactions. Three key functional characteristics were measured: 1) the maximum equivalent pressure output (MEPO) of the transducer; 2) the feedback gain margin (GM), which describes the maximum allowable gain before feedback occurs; and 3) the tympanic-membrane damping effect (D TM ), which describes the change in hearing level due to placement of the transducer on the eardrum. Results indicate that the tympanic-membrane transducer remains in place and is well tolerated. The system can produce sufficient output to reach threshold for those with as much as 60 dBHL of hearing impairment for up to 8 kHz in 86% of the study population, and up to 11.2 kHz in 50% of the population. The feedback gain margin is on average 30 dB except at the ear canal resonance frequencies of 3 and 9 kHz, where the average was reduced to 12 dB and 23 dB respectively. The average value of D TM is close to 0 dB everywhere except in the 2-4 kHz range, where it peaks at 8 dB. A new alternative system that uses photonic energy to transmit both the signal and power to a photodiode and micro-actuator on an EarLens platform is also described.