Allyn E. Hubbard - US grants

Evidence for an electromechanical process of intracochlear origin has been acquired by means of alternating current injection in scala media. A direct acoustic emission appears at the same frequency as the electrical current. In addition, the injected current modulates the sound pressure level of an input acoustic tone. We propose to characterize empirically this effect in the electrical and acoustical stimulus domains. We plan to explore the nature of the effect and its relation to auditory-nerve responses, using a variety of experimental manipulations. These include direct current injection in scala media, stimulation of cochlear efferents, two-tone suppression, cochlear temperature, ion-substitution, and sounds which produce acoustic trauma. The latter experiments involve SEM studies which will likely show concomitant damage to cochlear hair cells. As a working hypothesis, we believe that outer hair cells' (OHC) function includes not only transduction but also an active role in cochlear mechanics. The OHCs possess few, if any, afferent synapses; and yet OHC transduction does occur, as evidenced by the cochlear microphonic. We think that OHC transduction is involved in an electromechanical feedback process which affects basilar membrane response. We propose to construct computer simulations as the analytic embodiment of this idea. We intend to compare new data with model results.

The Massachusetts Microelectronics Center (M2C) plans to conduct a two-week (ten day) project-oriented workshop on the fundamentals of microelectronic systems education. This workshop is directed towards Electrical and Computer Engineering faculty with some experience in VLSI design but little or no experience with microelectronic systems building. The goal of the workshop is to equip the faculty with the resources necessary to develop and conduct undergraduate courses in microelectronics systems design that would culminate in rapid prototyping and testing of a system that incorporates multiple components and technologies with well-defined interfaces. Topics will include: the computer-aided engineering (CAE) approach to systems design, technology selection criteria, rapid prototyping, technology re-targeting, high-level description languages, multi-level simulation techniques, and systems design project which illustrates each stage of the design process with an emphasis on design trade- offs based upon implementation technology. A combination of public domain and commercial CAE tools is used. Working in project teams, attendees build a prototype system in FPGAs and then re-target the design specification to a standard-cell CMOS technology. One month after the workshop each attendee receives a set of the chips designed by his/her team and a test fixture for use in their undergraduate microelectronic systems design courses.

9320326 Mountain The cochlea is the complex structure in the inner ear that contains an elastic membrane, the basilar membrane, which oscillates in response to sound. The oscillations stimulate mechanosensory cells called hair cells, which send signals to the auditory nerve. A remarkable finding around 15 years ago showed that one group of hair cells, the outer hair cells, can themselves show motility, and so act as electromechanical elements that can modulate cochlear sensitivity. As a byproduct of that function, the outer hair cell activity is transmitted as acoustical energy back out of the ear, producing measurable sounds called otoacoustic emissions, which have been used by scientists and clinicians as a non-invasive tool to study cochlear function. This project uses electrophysiology, computer simulation, and measurements of the otoacoustic emissions to examine several novel hypotheses about how the basilar membrane vibration and the outer hair cell activity may be involved in normal cochlear function. It will specifically evaluate where the non-linearities in amplification occur in the cochlea, and whether the basilar membrane may have modes of oscillation different from the classical traveling-wave form. Results from this unique combined physiological and modeling approach will have an impact on all auditory neuroscience, and novel findings will have important impact not only on handling of hearing disorders, but on design of auditory communications, and on biomechanics and bioengineering. ***