Research
Research
Measuring and modeling behavior
We have developed a quantitative and principled analysis of motor behavior of C. elegans as it freely crawls on an agar plate. Behavioural data come from a custom built tracking microscope that captures and follows the motions of single worms crawling on agar for long time periods. We quantify behavior making no a priori assumptions of metrics, using techniques of machine vision, dimensionality reduction, and machine learning.
C. elegans neuroscience
To study the neuronal correlates of behavior, we use a variety of techniques to measure and perturb the activity of C. elegans neurons. Neurons can be ablated (e.g. killed) using pulsed laser light from a dye laser or a Ti:Sapphire laser. Signals from neurons can be measured using fluorscence microscopy using genetically encoded calcium indicators like GCamP or Cameleon. Neurons can be activated directly using channelrhodopsin. Neurons can also be developmentally ablated or functionally silenced using a variety of genetic techniques. The goal here is to correlate these neuronal perturbations with our behavior measurements to understand how these behaviors are implemented at the neuronal level.
Thermotaxis and associative learning
The nematode, C. elegans is thermotactic and prefers the temperature at which it was cultivated. When placed on agar plates in thermal gradients, worms will migrate toward their preferred temperature and near this temperature they will track isotherms with surprising accuracy (with 0.1 C). The thermal preference of worms is plastic. If placed at a different temperature in the presence of food, worms will acquire a new thermal preference in about 4 hours. By applying defined thermal stimuli to single worms using an IR laser and then following the behavior of the worm in time with the worm tracker, we are studying various components of the thermosensory behavior of C. elegans, including the impulse response, isothermal behavior, and general computational strategy.
Thermal pain response
We have developed an instrument that can track and programmatically stimulate C. elegans with an infrared laser. Some projects include: modeling the pain response, discovering genes and neurons involved in pain transduction, and using the pain response as a metric of health and agining.
Physics of search
What is the statistical foraging strategy of C. elegans? A common model of search is the random walk, in which the duration and direction of the movement is chosen randomly. In the absence of any sensory stimuli what statistical strategy will discover information ? Or more specifically, from what distribution should the organism choose the duration of its forward movements?
C. elegans mechanobiology
Animals the size of C. elegans live their lives at low Reynolds number. In a world with no inertia, these micro-swimmers and crawlers experience forces which are governed by vastly different physics from what we feel at our scale. When crawling on wet surfaces, for example, surface tension significantly overpowers gravity. How hard must organisms work in order to overcome these forces, and how do forces exerted by the environment affect the movement strategy and behaviour? Does the organism adopt an optimal strategy, or is it limited by bending its own body? Additionally, how does C. elegans sense external forces? The neural connectome for the worm is mapped, but what is the receptive field and the dynamics of the neurons involved? We have developed a micropipette platform in collaboration with the Dalnoki-veress lab (McMaster University) that allows us to lightly hold freely-behaving subjects and either administer or measure micronewton forces. This platform allows us to probe the organism's responses to very light touch stimuli and to measure the viscous drag which must be overcome in crawling locomotion.