23/01/2013 - 12:00 - Auditori PRBB

What big brains can learn from small brains

Scientific sessions, CRG Group Leader Seminars

Matthieu Louis

Sensory Systems and Behaviour Group, Systems Biology Programme, CRG


Unlike most of you probably, I did not start my career as a biologist. I was brought to life sciences after being trained as a theoretical physicist at the Free University of Brussels (ULB). Gradually my interest in dynamical systems theory and complex systems drove me from inert to living matter. For my PhD at the European Bioinformatics Institute (EMBL outstation), I studied the regulatory logic of simple gene networks. In the lab of Liisa Holm, I developed the first quantitative model for the process of sex determination in Drosophila - a textbook standard in developmental biology. At the end of my thesis, I was very fortunate to spend two months in the lab of Juan Valcarcel with whom I tested a prediction of my model. Juan's confidence in the ability of a "naive" physicist to generate any useful data at the bench allowed me to discover the joy of designing and conducting hypothesis-driven experiments. Motivated by this exhilarating experience, I joined the lab of Leslie Vosshall (Rockefeller University) to be trained in behavioral neurogenetics and sensory neuroscience. My postdoctoral research focused on the mechanistic basis of the peripheral encoding and the processing of olfactory stimuli in the Drosophila larva. Since I started my own group at the CRG in 2008, perception and orientation behavior have remained at the heart of our research. The main question my lab aims to address is how decision making and sensory-driven behaviors come about in terms of neural computation. 


Talk summary

Organisms ranging from bacteria to mammals follow chemical cues to locate food sources. Behavioral strategies employed for chemotaxis have been studied across phyla, but the neural mechanisms underlying the integration of olfactory inputs and its conversion into motor outputs remain poorly understood. In this group leader seminar, I will focus on our recent findings about the surprisingly high degree of information processing that takes place in a single olfactory sensory neuron (OSN) of the Drosophila larva. I will describe how we combine electrophysiology, optogenetics and computational modeling to clarify how dynamical olfactory signals are encoded by the peripheral olfactory system and how this information is likely to be converted into navigational decisions. 

I will discuss how the response of an OSN can be accounted for by a general class of regulatory motifs, the incoherent feedforward loop. The model reproduces two basic operations carried out by the OSN: temporal differentiation on short timescales and temporal integration on longer timescales. It also explains how these operations are combined to normalize the OSN activity and to confer the adaptive nature of the larval olfactory system. In the second part of the talk, I will discuss our progress towards the mapping of the neural circuitry that underpins the sensorimotor transformation directing larval chemotaxis. Altogether, this seminar will explore the link between neural computation at the sensory periphery and decision-making processes that direct navigation in a sensory landscape.