How does a worm move?
We start by investigating one of the most robust, and readily quantifiable behaviors: worm locomotion. C. elegans moves forward by generating and propagating sinusoidal body bending waves from head to tail. By developing and combining tools in optics, microfluidics, genetics and modeling, we have discovered a novel sensorimotor loop within the motor neurons that drives C. elegans locomotion. By making one body region directly respond to the bending of its anterior neighbor, C. elegans can propagate the body bending waves initiated from the head. Check the next two videos:
Here, the middle body region of a worm is constrained in a curved microfluidic channel. Through bend-sensitive coupling, the posterior body region is compelled to bend in the same direction as the anterior neighbor. To demonstrate that the bending of the tail emerged from the channel is due to active neuromuscular activities, we directly monitored calcium activities in worm muscles, see below. Yellow-red color indicates higher calcium activities in the muscle cells.
We are now primarily interested in the biophysical mechanisms by which C. elegans head motor circuit generates rhythmic activities. We are also interested in understanding the neural mechanisms underlying the flexibility of motor control: how worms can smoothly transition between different motor states (forward locomotion, backward locomotion and turns).
How does a worm taste?
For C. elegans and many other animals, it is the integration of internal representation of the movement (as I describe above) and the external sensory cues that drives adaptive motor behaviors. Together with Professor Linjiao Luo at Nanjing University, we are combining high throughput behavioral assays, optical neurophysiology, and genetic manipulation to dissect the sensorimotor circuit underlying C. elegans salt chemotactic behavior. Check this video:
Here, we monitor calcium activities in the primary chemosensory neuron ASER while the worm is navigating on a linear salt gradient. ASER calcium activity arises when the worm navigates down the NaCl gradient (moves towards right).
How does a worm think?
Whereas C. elegans has a compact nervous system, the sensorimotor transformation, which is implemented by ~ 100 interneurons, is much more sophisticated than we previously thought. We are developing new engineering tools for optical interrogation of the entire circuit in a freely behaving animal. The ability to probe every neuron in a circuit will allow us to develop theoretical ideas of how emergent properties of a network give rise to complex and context-dependent behaviors. For example, we have been able to perform whole brain imaging of neural activities in a freely behaving worm. Check the following video:
Here, different color indicates neurons at different depth of view.