Characterization of state dependent differences in central complex activity and its influence on motor control in the praying mantis (Tenodera sinensis)
Final Report Abstract
Complex tasks like hunting a moving prey through an unpredictable environment require high levels of motor sensory integration and decision making. It is crucial to determine when or where to move, to increase chances of finding food while at the same time avoiding detection by a potential predator. Feeding behavior differs drastically in the same animals when it is hungry compared to after feeding to satiety. Levels of various hormones are altered in response to such state changes. A successful hunt also requires the predator to focus its attention on only one of many potential prey objects, to avoid distractions by other movement in its surrounding. In the insect brain, the central complex (CX) is one target area where these complex integrations are likely to take place. The CX is a set of highly structured midline neuropils that are present in all arthropods and it has become the focus of numerous studies that have demonstrated its role in sensory processing of visual cues as well as its direct impact on controlling movement. My contributions to the CX story stem from multi-unit recording techniques that were de-veloped to record from the CX of tethered and freely moving cockroaches. My main accomplishment was to further develop and adapt these techniques for recording and analyzing CX activity in freely moving praying mantises as they respond to simulated prey. Much of my pro-gress has been in establishing critical baseline data. Over the course of my fellowship, I improved the method and obtained numerous successful recordings associated with both natural and arti-ficial prey stimuli. The finding of changes in hunting strategy from active stalking to an ambush behavior as it feeds, coupled with the finding that these changes could be mimicked with injection of insulin, provides a unique opportunity to add to the volume of information that is amassing in the field regarding the CX role in controlling complex behaviors. The experiments I have per-formed, demonstrate that CX circuits are involved in tracking prey as well as controlling the movements of the praying mantis. The observation that once the praying mantis focuses upon one prey, it ignores others moving through its field of view also suggests a role in attention. Quantifi-cation of these aspects of sensorimotor control, will advance the thinking regarding the CX role in these and other complex behaviors. The observations on changes in hunt strategy with satiety or insulin injection imply state dependent changes in control. Preliminary data suggesting that CX activity in targeting prey changes in parallel with behavioral hunting modifications point to either direct or indirect neuromodulation in CX circuits as a main factor in these adaptations. By identi-fying where and how insulin has its effect on hunting strategy, this will open up an entirely new avenue of investigation on this critical insect brain region. But the obtained results will impact our understanding beyond insect systems. One of the remarkable observations that have come out in recent years regards parallels between CX control systems in insects and various brain systems in mammals. Whether these similarities occur through deep homology or by convergence, the implications are striking. Wherever one looks for similarity, it is found. Recent findings of head direction cells in Drosophila and cockroach by other researchers, emphasize that similarities exist in navigation systems. With advantages provided by insects in identified neurons, genetic systems and hardiness of preparations plus the diverse be-haviors and niches that insects inhabit, such comparisons will be very important to future studies on animal navigation. Hence these findings regarding the behavioral consequences of neuromod-ulation in praying mantis CX will have wide ranging impact beyond insect studies. They might even have implications for development of adaptable robots.
