Multimodal integration in the feeding behaviors of predatory teleost fishes.

The search for useful model systems to study sensory processing in vertebrate nervous systems has resulted in many neuroethological studies investigating the roles played by a single sensory modality in a given behavior. However, animals behaving in a complex, three-dimensional environment receive a large amount of information from external and internal receptor arrays. Clearly, the integration of sensory afference arising from different modalities into a coherent 'gestalt' of the world is essential to the behaviors of most animals. Over the past several years researchers in my laboratory have examined the roles played by the visual and lateral line sensory systems in organizing the feeding behavior of two species of predatory teleost fishes, the largemouth bass, Micropterus salmoides and the muskellunge, Esox masquinongy. The free-field feeding behaviors of these fishes was studied quantitatively in intact animals and compared to animals in which the lateral line and visual systems had been selectively suppressed. The data show that both bass and muskie employ similar approach and strike behaviors. Vision is crucial to the initial detection of, and orientation to, prey. Lateral line and vision together determine the optimum distance and angular deviation for the initiation of a rapid strike toward the prey. Blinded animals are able to strike accurately at prey at very close ranges and small angular deviations, indicating that this modality presents sufficient information to direct the behavior during the final phases of the strike. The results demonstrate that there is a hierarchy of senses involved in feeding behavior, with different modalities playing critical roles in succeeding phases.

Information-processing demands in electrosensory and mechanosensory lateral line systems.

The electrosensory and mechanosensory lateral line systems of fish exhibit many common features in their structural and functional organization, both at the sensory periphery as well as in central processing pathways. These two sensory systems also appear to play similar roles in many behavioral tasks such as prey capture, orientation with respect to external environmental cues, navigation in low-light conditions, and mediation of interactions with nearby animals. In this paper, we briefly review key morphological, physiological, and behavioral aspects of these two closely related sensory systems. We present arguments that the information processing demands associated with spatial processing are likely to be quite similar, due largely to the spatial organization of both systems and the predominantly dipolar nature of many electrosensory and mechanosensory stimulus fields. Demands associated with temporal processing may be quite different, however, due primarily to differences in the physical bases of electrosensory and mechanosensory stimuli (e.g. speed of transmission). With a better sense of the information processing requirements, we turn our attention to an analysis of the functional organization of the associated first-order sensory nuclei in the hindbrain, including the medial octavolateral nucleus (MON), dorsal octavolateral nucleus (DON), and electrosensory lateral line lobe (ELL). One common feature of these systems is a set of neural mechanisms for improving signal-to-noise ratios, including mechanisms for adaptive suppression of reafferent signals. This comparative analysis provides new insights into how the nervous system extracts biologically significant information from dipolar stimulus fields in order to solve a variety of behaviorally relevant problems faced by aquatic animals.