Functional Overlap and Nonoverlap Between Lateral Line and Auditory Systems

Sound-producing and moving objects present a wide range of hydrodynamic and acoustic stimuli. The mechanosensory lateral line and inner ear of fishes share an evolutionary history and both utilize displacement-sensitive hair cells. However, despite their common embryological origin and similar sensory cells, there is amazingly little functional overlap between the inner ear and the lateral line. Both systems respond to low-frequency stimuli at short range, but the auditory systems are sensitive also to higher frequencies and are capable of detecting more distant stimuli. There is a great distinction in the mechanisms of stimulus transduction and the specific hydrodynamic properties relevant to each sense. The inner ear is capable of detecting both hydrodynamic forces and the minute particle fluctuations associated with far field acoustics, while the lateral line is sensitive only to hydrodynamic forces in the spatially inhomogeneous near field very close to the source. In addition, the lateral line can detect the long-lived, turbulent wake of swimming fish. Consequently, each sense is used differently in behavioral contexts such as predation and predator avoidance, orientation to currents, communication, and navigation. The pathways of information flow in the central nervous system are correspondingly discrete, with integration occurring in the midbrain and possibly in the telencephalon. The Mauthner network is an illustration of one type of integrative center that reflects an overlap of function, but the general differences in behavioral function of these two senses predict that substantial neuronal integration occurs only at higher levels.