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Benjamin Lindner

Bernstein Center Berlin,
Technische Universität Berlin

Benjamin Lindner has moved into the newly-renovated brick building in the center of the Charité Campus in May 2011. He took up a newly established professorship at the Bernstein Center Berlin at the Institute of Physics, Humboldt Universität zu Berlin. In the coming years, he will both continue his research and teach on the subject of the “Theory of Complex Systems and Neurophysics”.

benjamin lindner

© Private

Benjamin Lindner studied physics at the Humboldt University and did his PhD at the Institute of Physics with Lutz Schimansky-Geier on a topic within the theory of stochastic processes. It was also Schimansky-Geier who brought him in contact with neuronal models. “Neurobiology is an exciting field of application for the physics of nonequilibrium systems and the theory of random processes,” says Lindner.

From the viewpoint of theoretical physics, neuronal systems are composed of many molecules that are kept out of thermodynamic equilibrium by metabolism. This allows them to form structures with complex dynamics. Neuronal excitability and the generation of action potentials in nerve cells are a prime example of complex dynamics. However, the single components of the nervous system (e.g. receptor and nerve cells) are so small that random fluctuations can significantly influence their behavior. How do receptors or neurons process sensory information when complex nonlinear dynamics and neuronal noise interact? This question keeps Lindner and other theorists busy.

Lindner has investigated this question in abstract neuronal models and also in specific sensory systems, for example, in weakly electric fish and in the auditory system of locusts. In this connection, he prefers models that take relevant biophysical details into account but still permit an analytical approach: “As a physicist, I am interested in the mathematical mechanisms that underlie the experimentally observed properties.” In his view, simplifications of the model that are enforced by the mathematical analysis often contribute significantly to the gain of knowledge. This, of course, does not release him from the obligation of testing predictions of simple models by the use of computer simulations of more detailed models. “However, it is most satisfying when theoretical predictions are confirmed in the experiment,” explains Lindner.

A recent study by Lindner is devoted to ’channel noise’. The excitability of neurons, as well as properties like adaptation, rely on the opening and closing of specific ion channels in the cell membrane. At the same time, these channels contribute random perturbations (fluctuations). Moreover, the fluctuations stemming from different kinds of channels can have very different and measurable effects on the statistics of neuronal firing. Together with his Ph.D. student Tilo Schwalger and Jan Benda’s group at the Bernstein Center Munich, Lindner studies the implications of these findings. The developed mathematical model also allows for answering the reverse question: Which kind of ion channel dominates neural noise? This is highly interesting because for many neurons, the type and number of channels in the membrane is unknown. The model can thus potentially serve to indirectly estimate unknown parameters of the neuron (e.g. number and conductance of ion channels). An application of the theory to neuronal data, which were measured by Karin Fisch and Jan Benda in Munich in the auditory receptors of locusts, appears promising.

Although Benjamin Lindner has a preference for analytical methods, he believes in the necessity of interdisciplinary collaborations. During his three-year research period at the University of Ottawa (Canada), in the groups of Andre Longtin and John Lewis, he made his first contacts with experimentally working scientists. Despite some initial difficulties in communicating across scientific fields, he has learned a lot from this cooperation: “Experimentalists and theorists often have very different perspectives on the same phenomena. This makes the exchange sometimes complicated, but often stimulating and fruitful.” At the Bernstein Center Berlin, he seeks new collaborations with the resident experimenters.

benjamin lindner-haarzellen

Virtually coupled: hair bundle cells in the inner ear possess brush-like elongations, the so-called hair bundles (shown here in green). These are coupled to each other, leading to a better detection of oscillating signals such as sound. © Kai Dierkes, MPI for the Physics of complex Systems

After his return from Canada in 2005, Benjamin Lindner did research at the Max Planck Institute for the Physics of Complex Systems (Dresden). There he worked on the dynamics of sensory hair cells in the inner ear. By means of their ‘hair bundles’, hair cells register and transduce mechanical signals, e.g. sound, into electrical signals. In various hair cells it has been shown that hair bundles can spontaneously oscillate even without any external stimulation. This property makes hair cells suitable for the perception and amplification of periodic signals. Experiments on single hair cells, however, show that these oscillations are noisy, which reduces their amplifier characteristics significantly. Lindner, together with his Ph.D. student Kai Dierkes and with Frank Jülicher, Director at the Max Planck Institute in Dresden, could theoretically demonstrate that the mechanical coupling of hair bundles improves the signal gain of the hair cell. Such coupling can be found in the human cochlea. Biological support for the hypothesis came from an inventive hybrid experiment, a collaborative experiment with colleagues in Paris, Jérémie Barral und Pascal Martin. They coupled a biological hair bundle with two computer-simulated “virtual” hair bundles, and this resulted in improvement of the signal gain in the experimentally studied hair cell.

Of course, much of the theoretical results on the complex dynamics of neuronal systems are nowadays achieved in extensive computer simulations. However, new ideas are still developed with paper and pencil or with students and colleagues in front of a board. While his students have asked for whiteboards for their new rooms, Lindner prefers the classic style. Besides computer and pencil, his most important tool is the blackboard on the wall of his office.