Sensory Processing Research

BINAURAL HEARING: The study of binaural hearing concerns how and how well the ear and brain process information that arrives at two ears. In real-world settings, the information that arrives at the ears differs in terms of its timing and in terms of its intensity. It is these interaural differences that allow for the localization of sounds in space and for the detection and discrimination of signals in noisy backgrounds (e.g., speech in a background of noise). Several aspects of binaural hearing are the focus of research within the Department of Neuroscience. These range from the anatomical and physiological underpinnings of binaural processing to behavioral, or psychoacoustic measures in humans.

HEARING DIAGNOSTICS: Vibrations are generated by the normal hearing mechanism as part of its processing of sounds that impinge on the eardrum. That is, the ear makes sounds of its own. The measurement of these otoacoustic emissions can serve as a powerful diagnostic tool for evaluating the health, status, and function of the inner ear and the auditory system. Electrophysiological measurements offer another noninvasive means of evaluating the status of the hearing mechanisms. These are made by measuring electrical potentials at the scalp that occur in response to sounds. Within the Department of Neuroscience, investigators are involved in the development, refinement, and utilization of diagnostic techniques based on the measurement of Hearing Diagnostics.

RETINAL DEGENERATION: Retinal degeneration in humans primarily affects photoreceptors (rods and cones) in such diseases as retinitis pigmentosa and macular degeneration. The latter affects nearly 10 times as many people as Alzheimer's disease and is thus the most common neurologic disorder of humans. The other retinal neurons that die in glaucoma are the ganglion cells. Why these neurons die is a mystery since the defined mutations are not, for the most part, in crucial genes for cell viability (e.g. rhodopsin). Several model systems in various experimental animals exist (mice, rats, chickens, cats, dogs). Transgenic frogs are being explored as a model system because they have abundant rods and cones. They therefore provide a useful setting for studying cellular fratricide, the killing of similar cells that do not express the mutant protein. They are also quite inexpensive to generate and maintain in large numbers. Many models of retinal degeneration in frogs have been generated in just a few years. The attached figure illustrates the outcome of expressing a mutant dominant-negative from of rab8 (22N) under the control of the Xenopus opsin promoter. This transgene interferes with membrane protein transport in the rods. It kills the rods early (5d B) and the result is an all-cone retina within two weeks after fertilization (14d B). This offers numerous opportunities to study rod apoptosis and the rewiring of the retina and CNS in a frog genetically programmed to have both rods and cones with the rods deleted by genetic engineering. Figure legend: A and B. 5 day old tadpole retinas labeled for apoptotic cells (brown deposit) by the TUNEL assay. Note the numerous dying cells in the inner (INL) and outer nuclear (ONL) layers of the mutant retina. The dying nuclei in the INL are photoreceptor cells that have not yet completed their migration into the ONL in this immature retina. C and D. 14 day old tadpole retinas stained by H&E. Rod outer segments and cone outer segments are both present in the wt retina (C) but only cones are surviving in the mutant retina (D).