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Original Research Article
Precisely timed signal transmission in neocortical networks with reliable intermediate-range projections

1  Neuroinformatics and Theoretical Neuroscience, Institute of Biology-Neurobiology, Freie Universität Berlin, Germany
2  Bernstein Center for Computational Neuroscience Berlin, Germany
3  Bernstein Center for Computational Neurosciene, Albert-Ludwigs-University Freiburg, Germany
4  Neurobiology and Biophysics, Institute for Biology III, Albert-Ludwigs-University, Germany

The mammalian neocortex has a remarkable ability to precisely reproduce behavioral sequences or to reliably retrieve stored information. In contrast, spiking activity in behaving animals shows a considerable trial-to-trial variability and temporal irregularity. The signal propagation and processing underlying these conflicting observations is based on fundamental neurophysiological processes like synaptic transmission, signal integration within single cells, and spike formation. Each of these steps in the neuronal signaling chain has been studied separately to a great extend, but it has been difficult to judge how they interact and sum up in active sub-networks of neocortical cells. In the present study, we experimentally assessed the precision and reliability of small neocortical networks consisting of trans-columnar, intermediate-range projections (200 – 1000 µm) on a millisecond time-scale. Employing photo-uncaging of glutamate in acute slices, we activated a number of distant pre-synaptic cells in a spatiotemporally precisely controlled manner, while monitoring the resulting membrane potential fluctuations of a post-synaptic cell. We found that signal integration in this part of the network is highly reliable and temporally precise. As numerical simulations showed, the residual membrane potential variability can be attributed to amplitude variability in synaptic transmission and may significantly contribute to trial-to-trial output variability of a rate signal. However, it does not impair the temporal accuracy of signal integration. We conclude that signals from intermediate-range projections onto neocortical neurons are propagated and integrated in a highly reliable and precise manner, and may serve as a substrate for temporally precise signal transmission in neocortical networks.

Keywords: cell assembly, coincidence detector, cortex, dynamic photo stimulation, synaptic variability, temporal coding, rate coding

Citation: Nawrot M, Schnepel P, Aertsen A and Boucsein C (2009) Precisely timed signal transmission in neocortical networks with reliable intermediate-range projections. Front. Neural Circuits (2009) 3:1. doi:10.3389/neuro.04.001.2009

Received: 15 September 2008; paper pending published: 28 October 2008; accepted: 27 January 2009; published online: 10 February 2009.

Edited by: 
Michael Brecht, Humboldt University Berlin, Germany

Reviewed by: 
Fritjof Helmchen, University of Zurich, Switzerland
Carl Petersen, École Polytechnique Fédérale de Lausanne, Switzerland

Copyright: © 2009 Nawrot, Schnepel, Aertsen and Boucsein. This is an open-access article subject to an exclusive license agreement between the authors and the Frontiers Research Foundation, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.

*Correspondence: Clemens Boucsein, Neurobiology and Biophysics, Institute of Biology III, Albert-Ludwigs-University, Schaenzlestrasse 1, D-79104 Freiburg, Germany. email: clemens.boucsein@biologie.uni-freiburg.de
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