The processing of sounds starts in the cochlea, which is both a spectral analyzer and a mechano-electric transducer. The auditory information is then carried by the auditory nerve to the brainstem. Anatomically, these early stages of the auditory pathway show an organization that is very similar across mammalian species. Functionally, processing in this stage is characterized by a high level of temporal accuracy. Our aim is to arrive at a quantitative description of sound coding by the auditory periphery, and to link it to known performance in behavioral tasks. To this end, we perform experiments on normal hearing rodents (mongolian gerbils), in which we measure responses to computer-generated acoustic stimuli. This involves extracellular, single-unit recordings from the auditory nerve, cochlear nucleus, olivary complex and inferior colliculus, and in vivo patch-clamping in the auditory brainstem. In addition to neural recordings, we measure mechanical responses of the inner ear using a laser vibrometer.
Cochlea. Due to its vulnerability and poor accessibility, the cochlea is still poorly understood. We record sub-nanometer vibrations of the basilar membrane in the sensitive ears. By comparing responses between adjacent locations, we analyze the propagation properties of traveling waves and their dependence on sound intensity. Our aim is to understand the physics underlying frequency sensitivity and dynamic range compression by the cochlea.
Masking. An important ability of the auditory system is the detection of sounds in noisy environments. When the noise is too loud, the sound is no longer audible and is said to be "masked." Much behavioral work has been devoted to auditory masking, but its neural correlates are largely unknown. We aim to systematically collect auditory nerve responses to stimuli used in behavioral masking studies, and to derive the limits of dection imposed by the auditory periphery.Timing. Some aspects of hearing, notably spatial hearing, demand a (sub-millisecond!) temporal precision that is much better than achieved by individual auditory nerve fibers. The information of multiple fibers is somehow integrated at the stage of the cochlear nucleus. It is our aim to find out the mechanisms behind this integration by measuring responses of the cochlear nucleus and comparing them to those of the auditory nerve.
Localization. Sound localization involves the detection of tiny differences between the sounds impinging on the two ears. This interaural comparison takes place in the olivary complex. The general mechanisms are known, but data are scarce because extracellular recordings from these binaural nuclei are difficult. We aim to use in vivo patch-clamping in the olivary complex in order to characterize its monaural inputs and to understand the mechanisms of the binaural comparison itself.