Central Processing of Lateral Line Information

Abstract

With the lateral line system, fish and aquatic amphibians detect minute water motions. The hydrodynamic information that is received by the lateral line sense organs, the neuromasts, is represented by the activity of afferent nerve fibers and is analyzed by the brain to determine identity and location of a source of hydrodynamic disturbance. This chapter presents our current knowledge on the processing of various hydrodynamic stimuli at different levels of the ascending lateral line pathway. Different stimuli have been used to study the function of central lateral line units, including dipole stimuli, moving objects, bulk water flow, and vortex streets. Compared to primary afferent nerve fibers, most central units are less sensitive to dipole stimuli and exhibit more complex spatial receptive fields and highly selective responses to moving objects. When exposed to bulk water flow, flow-sensitive central units may increase or decrease their ongoing discharge rate. As a consequence, their responses to dipole stimuli or moving objects may be masked. When stimulated with a vortex street, central units may represent the vortex shedding frequency in their activity. Anatomical studies have uncovered somatotopic representations of the lateral line periphery in various brain regions. Physiological data, however, that are indicative of a systematic representation of hydrodynamic information such as source location or bulk flow velocity in the form of a central map are scarce. More studies are needed to uncover the computational rules and the circuit diagrams implemented in the central lateral line.