Research Group "Computational Neurobiology"

Prof. Andreas V. M. Herz

Using a combination of experimental and theoretical approaches, the group studies various aspects of neural dynamics and signal processing, and has close ties with the junior research groups ''Neural Computation'' led by Laurenz Wiskott "Theoretical Neuroscience" led by Richard Kempter.

Our studies are part of the larger Computational Neuroscience Initiative in Berlin that includes groups from the Charite, Humboldt University, Technical University, Free University, Fraunhofer FIRST, the Max-Delbrueck Center and the Wissenschaftskolleg zu Berlin.

Background:

Most neurons use action potentials, brief and uniform pulses of electrical activity, to transmit information. An action potential is generated when the membrane potential of a neuron reaches a threshold value. The action potential then travels down the axon toward synapses terminating at postsynaptic neurons where it initiates postsynaptic currents that summate to trigger (or inhibit) new action potentials.

A sequence, or 'train', of action potentials may contain biologically relevant information based on rather diverse coding schemes. In motor neurons, for example, the strength at which an innervated muscle is flexed depends solely on the 'firing rate', the average number of action potentials per unit time (a 'rate code'). At the other end of the spectrum lie complex temporal codes that use the precise timing of single action potentials. Such temporal codes may be locked to an external stimulus such as in the auditory system, or be generated intrinsically by the neural circuitry.

The wide range of coding schemes raises a number of questions. What is the temporal precision of signals sent out by a given neuron? Do all of its numerous postsynaptic target cells receive the same information? If not, what determines the individual signal? How can postsynaptic neurons read out the information? What is the functional relevance of correlations in the action potentials of several neurons? Which processes could generate the neural circuitry required for precise temporal codes? How can a signal based on the precise timing of action potentials be propagated from neuron to neuron? Questions of this kind are investigated by the group in various projects, ranging from data analysis to theoretical studies.

Synchronization processes and related dynamical phenomena in neural systems are being studied by a number of experimental groups in Berlin, opening up the possibility for close collaborations between theorists and experimentalists. Apart from the analysis of specific animal models, comparisons between different systems will lead to new insights about neural codes and their evolutionary history.

Current Projects include:

Discrimination of acoustic communication signals by grasshoppers - a first step toward sexual selection
Samuel Glauser and Martin Stemmler - in cooperation with the group of Bernd Ronacher (Humboldt University)

Optimal stimulus ensembles for efficient coding in sensory neurons
Tim Gollisch and Olga Kolesnikova in cooperation with Christian Machens (Cold Spring Harbor)

Identification of single steps in sensory signal-transduction chains
Tim Gollisch and Alexander Wolf

Burst coding in an insect auditory system
Felix Creutzig

Dynamics and function of subthreshold oscillations in the hippocampus
Susanne Schreiber and Wiebke Krambeck - in cooperation with the group of Uwe Heinemann (Charité)

Processing of temporally structured stimuli in the hippocampus
Susanne Schreiber - in cooperation with the group of Dietmar Schmitz (Charité)

Phase reset or linear summation? Qualitative models for large-scale brain activity
Siamac Fazli and Tim Oppermann - in cooperation with the group of Arno Villringer (Charité)

Internet Plattform Neuroinformatik
Thomas Förster and Raphael Ritz

Jan Benda [now in the lab of Andre Longtin in Ottawa]
Roberto Fernández Galán [now in the lab of Bard Ermentrout at Carnegie Mellon]
Christian Machens [now in the lab of Carlos Brody in Cold Spring Harbor]

Irina Erchova [now in the lab of Daniel E. Shulz in Gif-sur-Yvette]
Irina Kopysova [now at UNIC in Gif-sur-Yvette]
Ines Samengo [now back in San Carlos de Bariloche]
Hartmut Schütze [now in Magdeburg]

Our projects are supported by the Deutsche Forschungsgemeinschaft through the 'Sonderforschungsbereich' Theoretical Biology, the 'Graduiertenkolleg' Signal Cascades in Living Systems and the 'Graduiertenkolleg' Dynamics and Evolution of Cellular and Macromolecular Processes. Additional funding is provided by the Studienstiftung des Deutschen Volkes, the Gottlieb Daimler- und Karl Benz-Stiftung, and the Boehringer Ingelheim Fonds. The "Internet Plattform Neuroinformatik" is funded through the Bundesministerium für Bildung und Forschung.