Regensburg 2002 – scientific programme

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SYPH: Physik im Hirn - Physical Approaches to Brain Function

SYPH IV: HV IV

SYPH IV.1: Invited Talk

Wednesday, March 13, 2002, 16:30–17:10, H2

Neuronal dynamics and cortical signal processing — •Klaus Pawelzik — University of Bremen, Institute of Theoretical Physics
, Kufsteiner Str., D-28334 Bremen

Information processing in neocortex can be very fast, indicating that neuronal ensembles faithfully transmit and process rapidly changing signals. In this talk I address the question how fast a population of cortical neurons can process an input signal in its firing rate. While in principle a rate can change on arbitrary short time scales, the biophysical properties of individual neurons and collective phenomena in the population may substantially limit the speed at which a graded signal can be represented by the activity of an ensemble. We combined theoretical analysis and intracellular recordings to show that encoding signals in the variance of uncorrelated synaptic inputs to a neocortical ensemble enables faithful transmission of very fast signals. In contrast we find that encoding signals in the mean of the input currents is subject to temporal filtering. Furthermore, we analysed the role of neuronal diversity for the short term coding properties of neuronal populations and determined that it may substantially improve the representation of a stimulus. Finally I will discuss a novel hypothetical role for the feedback dynamics in cortex: the optimal iterative estimation of the causes underlying the stream of input stimuli.