Professor Dennis M. Freeman is a Principal Investigator in the Research Laboratory of Electronics (RLE) at the Massachusetts Institute of Technology (MIT). He received his B.S. from the Pennsylvania State University in 1973, and his S.M. and Ph.D. from MIT in 1976 and 1986 respectively.
Professor Freeman’s research is aimed at understanding the cellular and molecular origins of the remarkable properties of human hearing. Human hearing is sensitive: we can detect sounds that vibrate the eardrum less than the diameter of a hydrogen atom. It is selective: we can distinguish as many as 30 different frequencies within the interval of a single musical semitone. And it is highly nonlinear: sounds pressures ranging over 7 orders of magnitude are ultimately compressed to the less than two orders of magnitude available for neural communication. Unfortunately, the cellular and molecular mechanisms underlying these remarkable properties are poorly understood, and therefore remediation of hearing deficiencies has focused more on correcting the symptoms than on correcting the underlying causes.
To improve our understanding of basic mechanisms of hearing, Professor Freeman’s group has pioneered the measurement of sound-induced motions of sensory receptor cells and accessory structures in the inner ear. His group has recently discovered that the tectorial membrane, which is a gelatinous structure that overlies the mechanically sensitive sensory hairs of hair cells, supports waves of motion that contribute to both sensitivity and selectivity of hearing. Changes in these waves have been shown to underlie deficits in hearing that have previously elluded explanation.