To survive, animals must be capable of orienting toward food and mates, while avoiding predators, and negotiating obstacles. These tasks require complex and often directed behaviors. For instance, a cockroach may sense an obstacle in its path, and have to adjust its posture and make targeted limb movements to surmount the obstacle (Watson et al., 2002). This seemingly simple task requires enough sensory information about the obstacle to initiate the proper behavior, postural adjustments, and re-targeting of limb motions such that the limb will reach the top of the obstacle. Despite their small brains, invertebrates such as the insects and leeches are able to perform tasks such as these. How is this sensory information integrated with motor information to guide these behaviors?
My work on cockroaches examined what sensory information is necessary to guide obstacle negotiation behaviors and used discrete lesions to investigate how the brain is involved in command formation and sensory processing. This work focused on a midline neuropil of the insect brain known as the central complex. We were able to use behavioral changes resulting from lesions of specific brain regions to characterize the involvement of subregions of the central complex in obstacle negotiation behaviors.
This investigation of the formation of motor commands and sensory processing occurred at the level of the brain region prompted the desire to investigate these same concepts at the level of the neural network. This resulted in a move to the leech which has a much simpler nervous system. Even so, leeches are predators which are able to localize prey using their large array of visual and mechanosensors. How does such a simple nervous system encode direction, filter information, and guide locomotion? These are questions I am working to answer using behavior, physiology, and histology. Lately, I have been focusing on the leech brain (pictured to the left). This structure of a mere 2000 cells is able to combine information from the 10 head eyes to determine prey direction and guide locomotion. If the prey should move the leech's sensory system is used to update its direction of movement seemingly seamlessly. Needless to say, this is a complex event, which, is able to be created using a seemingly simple 2000 cell brain. We are busily determining the anatomy and physiology that allows for this complex behavior.