Neural coding. We are interested in neural coding and in systems aspects of circuit function in the brain. Over the past 12 years, this lab’s work has focused on circuit dynamics and their possible relevance for coding and representation, using the olfactory system as a model (Laurent, Science, 1999; Nature Reviews Neuroscience, 2002). Our approach is mainly experimental, but relies also on tight interactions with theory (Rabinovich et al., Physical Review Letters, 2001) and numerical simulations (Bazhenov et al., Neuron, 2001; 2005). Our experimental work combines electrophysiological, imaging, genetic and behavioral techniques. The systems we study are chosen for their small brains (insects, such as Drosophila, locusts, honeybees, and zebrafish), so as to facilitate—we hope—the discovery of functional principles of widespread relevance.

Oscillations. Oscillatory synchronization of neurons is a widespread phenomenon, observed in animals from slugs to humans. Using insect olfaction, we have been able to establish the functional relevance of such emergent circuit properties in that system (MacLeod and Laurent, Science, 1996; Stopfer et al., Nature 1997; MacLeod et al., Nature, 1998), and are beginning to understand its computational significance (Perez-Orive et al., Science, 2002; Journal of Neuroscience, 2004).

Transient and fixed-point dynamics.  Using fish (Friedrich and Laurent, Science, 2001) and insect olfaction (Wehr and Laurent, Nature, 1996; Laurent et al., Journal of Neuroscience, 1996), we have examined in detail the dynamics of odor responses in first order central neurons (mitral cells or projection neurons). We found that response dynamics can be complex, with transient phases and fixed-point attractors; yet, the relevant phases (when examined from the targets’ point of view) are the dynamic ones and paradoxically, not the fixed points (Mazor and Laurent, Neuron, 2005). Dynamic periods also happen to be those in which representations are best separated. These results have interesting potential implications for the manner in which electrophysiological and imaging data should be interpreted, and for our understanding of neural codes.

Drosophila electrophysiology. Using Drosophila as a model system for olfactory research and in vivo electrophysiology, we hope to bridge the gap between circuit structure and computation (Wilson et al., Science, 2004; Wilson and Laurent, Journal of Neuroscience, 2005).

Neuronal computation. We are also interested in the biophysics of neuronal computation. Recently, we focused on dendritic processing in a visual neuron sensitive to looming objects. We found that its integrative properties (spike output) approximates a multiplication of two factors, each function of angular size and velocity of the approaching object’s image on the retina (Hatsopoulos et al., Science, 1995; Gabbiani et al., Journal of  Neuroscience, 1999; 2001). By examining the intrinsic and synaptic properties of this neuron, we are getting closer to understanding the biophysical mechanisms that can generate a multiplicative computation (Gabbiani et al., Nature, 2002).

Publications.  A list of relevant publications and downloadable PDFs can be found in the PUBLICATIONS section above.

More Detail. Follow this link to figures and movies of projection neurons and other work.