How the brain controls behavior: Using flies to study motor control at the circuit level – 9/25/2017

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Claire McKellar
Janelia Research Campus/HHMI


Investigating how the nervous system controls complex behaviors in simple animals could reveal mechanisms that are fundamental to behavior across species. Cutting-edge genetic tools in flies allow control over multiple neuron types, giving access to a circuit-level view of behavioral control. I am addressing two important questions about behavioral control. 1) How are complex behaviors formed from sequences of motor actions? A good model of a behavioral sequence is Drosophila male courtship, which consists of discrete actions in a probabilistic sequence. I have found a key pathway in the fly brain that generates a sequence of courtship actions. It uses a threshold-based mechanism theorized for more than 50 years, but not previously discovered in the control of sequences. 2) How can a motor action be flexibly reused in multiple behaviors? Both courtship and feeding use the motor action of proboscis extension, a reaching-like motion towards a female or to food. How is that multifunctionality encoded in the architecture of the nervous system? I have used genetic tools to acquire control of every type of proboscis motor neuron, and to examine their relationship to other circuit components. This unprecedented control over an appendage lays the foundation for a new model system for directed reaching, a behavior usually studied in higher animals to understand targeted behavior. I’ve found striking kinematic parallels in reaching towards targets in humans and flies. Linking up proboscis motor outputs with the command circuitry for courtship and feeding will reveal principles of how dedicated circuits for separate behaviors can converge on shared motor outputs, a fundamental problem in understanding motor control.