Laurent Department

Computation in three-layered cerebral cortex
Our laboratory is interested in the behavior, dynamics and emergent properties of neural systems (typically, networks of interacting neurons or neuron populations), especially as these properties relate to neural coding and sensory representation. The lab focuses principally on olfactory and visual areas, combining experiments, quantitative analysis and modeling techniques. We tend to use "simpler" experimental systems such as the brains of insects, fish and reptiles to facilitate the identification, mechanistic characterization and computational description of functional principles.

When at the California Institute of Technology (between 1990 and 2009), the lab focused on dendritic computation in single neurons (gain control in sensory-motor local neurons , dendritic multiplication in large field visual neurons), on central olfactory coding and on some aspects of visual processing (looming detection). The experimental parts of this work were carried out in locusts, Drosophila, honeybees, zebrafish and rat.

Since moving to the Max Planck Institute for Brain Research in Frankfurt, the lab's experimental focus has moved to reptilian cortex, with an emphasis on olfactory and visual areas. The choice of this experimental system is guided by several reasons:

(1) Simplicity: Reptilian cerebral cortex has a relatively simple architecture, at least when compared to that of mammalian isocortex: reptilian cortex contains only three layers, of which only two (LI and LIII) are neuropilar and mainly synaptic; in this it is similar to mammalian hippocampus and to olfactory cortex (archi-/paleocortices). As in piriform cortex and hippocampus also, only layer II is enriched in cell bodies, containing the somata of spiny pyramidal cells. Finally, reptilian cortex also appears to be relatively homogeneous across sensory areas. 

(2) Evolution: Turtles are among the closest links to the stem amniote ancestors of today's mammals, reptiles (and birds). While it is most likely that today's turtles evolved from, and are thus not identical to their ancient ancestors, it remains that understanding the computational architecture of their cortex could help reveal the ancestral design of mammalian olfactory cortex and hippocampal formation and more generally, reveal the functional logic of the earliest modules or computational building blocks of cerebral cortex in vertebrate evolution.

(3) Experimental: Turtles are aquatic animals; they have evolved diverse metabolic mechanisms for resistance to anoxia, making brain tissue particularly suitable to in vitro experimentation.

(4) Behavior: Finally, despite a reputation for indolence if not somnolence (turtles are, like all reptiles, poikilotherms and tend to enjoy sitting in the sun), many turtle species are predatory, active and highly visual as well as olfactory. They can be trained in a variety of experimental paradigms. They thus offer an excellent behavioral repertoire for combination with experimental neurobiological techniques.

Experimental Approaches
The lab's research is centered on neurophysiological approaches and on experimental data. We combine single-cell electrophysiological techniques (whole-cell patch-clamp, intracellular, extracellular recordings), in vivo tetrode recordings, imaging (intrinsic, calcium, multi-photon) with modern molecular techniques (viral infections and gene transfer, photo-activation and silencing).

A large component of the lab's expertise is also based on quantitative models and data analysis, carried out "in house". Much of our prior work has benefited greatly from close and long-lasting collaborations with physicists, modelers and other quantitative experimentalists, with whom ideas and concepts were developed, tested and refined. Among them are Misha Rabinovich (Physics, UCSD), Henry Abarbanel (Scripps, UCSD), Maksim Bazhenov (Salk, now UCR), Terry Sejnowski (Salk Institute), Markus Meister (Harvard University), Maria Geffen-Neimark (Rockefeller University). Similar collaborations are being set up with theorist colleagues at neighboring institutions (Frankfurt Institute of Advanced Studies; Physics Department, Goethe University; Center for Scientific Computing, Goethe University).

Our laboratory at the new MPI for Brain Research is designed as a large, open space, and to overlap with the laboratory of Erin Schuman. With this interdigitation of lab spaces, we try to foster exchanges of techniques and ideas between our related domains of expertise and aim to create a highly collaborative environment.