Many neural networks dynamically transition from one type of activity to another. Most studies designed to determine how task switching occurs at the circuit or cellular/molecular level have emphasized the `decision making' process that initiates one type of activity and terminates another. This research often targets `higher order' or command-like neurons. Our research demonstrates that this approach has limitations. Thus, the dynamics of task switching can be greatly impacted by the ability of a network to respond to a change in `command'. The circuit that we study is similar to many others in that its activity is configured and reconfigured by modulatory neurotransmitters that exert effects that persist and create an implicit form of memory. An important general question our research addresses is; how will persistent modulation impact task switching? We address this question in the situation where the switch is between two types of `antagonistic' motor programs. Initial studies of task switching characterized a situation where there was a `negative' effect, i.e., persistent effects of neuromodulation made it impossible to task switch immediately. This `task switch cost' was observed in a situation in which it is presumably beneficial. Namely, we demonstrated that a feeding network that had repeatedly generated egestive motor programs could not rapidly switch and generate ingestive motor activity. Research proposed in this application addresses a new issue; is there a situation in which persistent neuromodulation can have the opposite effect and be `beneficial' for task switching? Taken together previous and preliminary data strongly suggest that the answer to this question is yes. Proposed experiments are designed to seek further support for this idea. In broad terms our research will provide insight into circuit and cellular/molecular mechanisms that can facilitate or impede task switching. These mechanisms are of considerable general interest since task switching is essential for most species (including humans) to cope with changes in the external environment.
The experiments proposed in this application focus on a type of task switching in which an ongoing behavior is temporarily interrupted by a brief switch to a distinctly different type of motor activity. In this situation a quick, efficient return to the original behavior is often advantageous. Proposed experiments will characterize circuit and cellular/molecular mechanisms that facilitate this type of transition.
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