MODELING AND MEASURING LATERAL-LINE EXCITATION PATTERNS TO CHANGING DIPOLE SOURCE LOCATIONS

In order to determine excitation patterns to the lateral line system f rom a nearby 50 Hz oscillating sphere, dipole flow field equations wer e used to model the spatial distribution of pressures along a linear a rray of lateral line canal pores. Modeled predictions were then compar ed to pressure distributions measured for the same dipole source with a miniature hydrophone placed in a small test tank used for neurophysi ological experiments. Finally, neural responses from posterior lateral line nerve fibers in the goldfish were measured in the test tank to d emonstrate that modeled and measured pressure gradient patterns were e ncoded by the lateral line periphery. Response patterns to a 50 Hz dip ole source that slowly changed location along the length of the fish i ncluded (1) peaks and valleys in spike-rate responses corresponding to changes in pressure gradient amplitudes, (2) 180 degrees phase-shifts corresponding to reversals in the direction of the pressure gradient and (3) distance-dependent changes in the locations of peaks, valleys and 180 degrees phase-shifts. Modeled pressure gradient patterns also predict that the number of neural amplitude peaks and phase transition s will vary as a function of neuromast orientation and axis of source oscillation. The faithful way in which the lateral line periphery enco des pressure gradient patterns has implications for how source locatio n and distance might be encoded by excitation patterns in the CNS. Pha se-shift information may be important for (1) inhibitory/excitatory sc ulpting of receptive fields and (2) unambiguously encoding source dist ance so that increases in source distance are not confused with decrea ses in source amplitude.