The behaviour of an animal arises from the interplay between its environment, its experience, and intrinsic properties of its neural circuits.

Unique to C. elegans is its compact nervous system consisting of just 302 neurons with reproducible location, functions and synaptic connectivity. The complex network made of 8000 synapses and xxxgap junctions is entirely described at the EM resolution.

Diagram of connectivity, yellow=sensory neurons, blue= interneurons (J White et al 1984)

C. elegans senses and discriminates hundreds of different environmental cues, mostly chemicals, and generates behavioural sequence in response to them. The artificial activation (e.g. Chanelrhodopsin II ) of the sensory neurons physiologically responsive to these cues are sufficient to generate these same behavioural sequence as the cues itself. For example, sensory neurons activation are often associated with simple behavioral programs, such as attraction or repulsion.

The function of the nervous system is specified by its structure, the precise synaptic connections between neurons in circuits. This principle drives the new field of connectomics which ambition to understand the brain function starting from the brain connectivity patterns. However this neuronal circuitry of C. elegans is known since the 80’s and we are still far to understand how such a simple circuitry works. Recent works have highlighted the significance of neuromodulation and GAP junctions to understand how to make sense of the circuit.

One of the interesting observations is the constant connectivity pattern C. elegans exhibit. Nervous system need to remain flexible, able to learn or to adapt. In mammals, it is argued that this occurs through synaptic rearrangement. We are using genetic and imaging methods to study how reliable behavioural responses to specific cues are generated and how plasticity is maintained without synaptic rearangement.