Lateral Line Research: the Importance of Using Natural Stimuli
159
Using moving object stimuli one immediately learns that some higher-order
lateral line neurons show very specific response properties. Many units respond to
a moving object with only a few spikes (MUller et al. 1996; Wojtenek et al. 1998),
some units are inhibited while the object moves by (Mogdans et al. 1997). In terms
of spike number, medullary units are usually not directionally sensitive. However,
toral units often respond only if the object moves in a certain direction (Fig. 4B).
With a dipole stimulus units of this type would not have been discovered. Recent
physiological experiments with moving objects indicate that there is a lateral line
map in the torus semicircularis of fish. Units in the anterior lateral torus respond
while the object moves along the anterior part of the fish. Units at increasingly
more posterior locations respond while the object moves along increasingly more
caudal parts ofthe fish (Bleckmann and Zelick 1993, Plachta unpubl.).
8 Behavior
Animals increase their biological success by reacting to subtile aspects of the
environment (Krebs and Davis 1991). Besides visual, acoustic, and olfactory cues,
lateral line input is the basis for many behavioral decisions. Hydrodynamic input
is used, for instance, for prey detection, predator avoidance, intraspecific communication, schooling behavior, object discrimination, and wave source localization (Bleckmann 1994).
Some fish use the dispersion and damping properties of the water surface to
determine the distance to a surface wave source, thus indicating that they exploit
the complicated physical properties of the water surface for prey localization
(Bleckmann et al. 1989). However, in most experiments the behavioral tasks the
fish had to fulfill were quite simple, i.e., most behavioral experiments were not
designed to elucidate the full behavioral capabilities of fish to discriminate
complex water motions under still and running water conditions.
9 Background Noise
In order to fully understand the capabilities of the lateral line we need more behavioral and physiological experiments in flow tanks. Water currents are a dominant
and pervasive feature of many aquatic environments. Montgomery et al. (1997)
nicely showed that the superficial lateral line system of fishes controls rheotaxis at
low current velocities. Engelmann (unpubl.) recorded the responses of primary
lateral line afferents of goldfish to a dipole stimulus under both still-water and
running water conditions. Under stillwater conditions all units responded highly
sensitively and phase-locked to sinusoidal water motions. Without a frequency
analysis responses from superficial and canal neuromasts could hardly be distinguished. However, under running water conditions (background water velocity 10
159
Using moving object stimuli one immediately learns that some higher-order
lateral line neurons show very specific response properties. Many units respond to
a moving object with only a few spikes (MUller et al. 1996; Wojtenek et al. 1998),
some units are inhibited while the object moves by (Mogdans et al. 1997). In terms
of spike number, medullary units are usually not directionally sensitive. However,
toral units often respond only if the object moves in a certain direction (Fig. 4B).
With a dipole stimulus units of this type would not have been discovered. Recent
physiological experiments with moving objects indicate that there is a lateral line
map in the torus semicircularis of fish. Units in the anterior lateral torus respond
while the object moves along the anterior part of the fish. Units at increasingly
more posterior locations respond while the object moves along increasingly more
caudal parts ofthe fish (Bleckmann and Zelick 1993, Plachta unpubl.).
8 Behavior
Animals increase their biological success by reacting to subtile aspects of the
environment (Krebs and Davis 1991). Besides visual, acoustic, and olfactory cues,
lateral line input is the basis for many behavioral decisions. Hydrodynamic input
is used, for instance, for prey detection, predator avoidance, intraspecific communication, schooling behavior, object discrimination, and wave source localization (Bleckmann 1994).
Some fish use the dispersion and damping properties of the water surface to
determine the distance to a surface wave source, thus indicating that they exploit
the complicated physical properties of the water surface for prey localization
(Bleckmann et al. 1989). However, in most experiments the behavioral tasks the
fish had to fulfill were quite simple, i.e., most behavioral experiments were not
designed to elucidate the full behavioral capabilities of fish to discriminate
complex water motions under still and running water conditions.
9 Background Noise
In order to fully understand the capabilities of the lateral line we need more behavioral and physiological experiments in flow tanks. Water currents are a dominant
and pervasive feature of many aquatic environments. Montgomery et al. (1997)
nicely showed that the superficial lateral line system of fishes controls rheotaxis at
low current velocities. Engelmann (unpubl.) recorded the responses of primary
lateral line afferents of goldfish to a dipole stimulus under both still-water and
running water conditions. Under stillwater conditions all units responded highly
sensitively and phase-locked to sinusoidal water motions. Without a frequency
analysis responses from superficial and canal neuromasts could hardly be distinguished. However, under running water conditions (background water velocity 10