My research focuses on sensorimotor systems and the control of behavior in humans and animals. The ultimate goal is to understand how sensory elements, central nervous system circuits, and the skeletomuscular apparatus each contribute to movement. Exteroceptive and proprioceptive systems provide information on the environment and the state of the body. The physics of the environment conditions the available sensory stimuli. Circuits within the central nervous system both generate autonomous motor commands and make adjustments based on sensory inputs. The properties of muscles, the biomechanics of the skeletomuscular system, and the physics of the body's interaction with the surroundings transform motor commands and determine the actual movement. Thus, combined study of all three elements is essential.
Currently we are focussing on the control of prey-capture in the aquatic African Clawed Frog, Xenopus laevis. The ease with which the orientation behavior have made this a good model system for neuroethology--the study of the neural control of behavior. This animal orients towards prey that it can see, but like fish, it can also find prey in the dark or in opaque water using its lateral line system. The figure at the left illustrates a turn towards the source of waves on the surface of the water.
The lateral line system begins with an array of hair cells--sensory receptors like those of the inner ear--distributed over the body that is stimulated by water movement that, for example, are produced by objects falling into the water. Neural activity from these peripheral sensory receptors is processed in the hindbrain and then in the midbrain to produce a map or ordered representation of stimulus direction in a part of the midbrain called the tectum.. In the part of the map that has been studied, neurons at each location in the map respond best to waves coming from one particular direction on the surface of the water. A similar map of the directions of visual stimuli is located in more dorsal layers of the tectum and the two maps are in register--visual stimuli and lateral line stimuli coming from the same direction elicit activity at the same location of the tectum. This fact and the pattern of output connections of the tectum to motor control centers suggest that the tectum serves as a sensorimotor interface where sensory inputs from different sensory systems converge to a common pathway to elicit a turn towards the stimulus location..
Recently we completed a behavioral comparison of orientation to visual and lateral line stimuli by comparing turn angle to stimulus angle. The results supported this notion; the accuracy and precision of the turn using either sensory system is similar, as one would expect if it is controlled by similar sensory maps and common downstream motor circuits. However, the study also illuminated some of the differences in the function of the two systems. For example, the lateral line system is truly omnidirectional whereas the visual system is more apt to detect stimuli in front of the animal. Conversely, responses to visual stimuli are more apt to include a strike at the prey.