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Seminars & Lectures

* TITLE

Cortical Plasticity and the Cortical \"Operating Regime\"

* SPEAKERS

Name	Affiliation	E-mail
Klaus Obermayer	Bernstein Center for Computational Neuroscience and Berlin Univ. of Tech.	swan(at)postech.ac.kr

* HOST(Applicant)

Name	Affiliation	E-mail
-

* DATE / TIME

2007-08-31, 3:00 - 4:30 p.m.

* PLACE

APCTP Headquarters, Pohang, Korea

* ABSTRACT

In my talk I will first discuss results of developmental perturbations imposed on the visual system of adolescent cats through retinal lesions (cf. [1]). Using a computational model of visual cortical responses, I will show that the lesion induced changes of neuronal response properties are inconsistent with the common assumption that the underlying plasticity of intracortical connections is dependent on the temporal correlation of pre- and post-synaptic action potentials (\"Hebbian\"

correlation dependent plasticity). They are, however, consistent with the hypothesis that this plasticity is dependent upon the temporal order of pre- and post-synaptic action potentials (\"causal\" spike timing-dependent plasticity). Spike timing-dependent plasticity - in contrast to correlation dependent (Hebbian) changes - causes visual cortical receptive fields to converge by creating a competition between neurons for the control of spike timing within the network. The spatial scale of this competition appears to depend on the balance of excitation and inhibition and and can in principle be controlled by synaptic scaling type mechanisms. This reveals a novel way by which the capacity of cortical learning rules to transfer response properties between neurons can be effectively switched on and off.

But what is the cortical \"operating regime\" to begin with? Using a computational model of a cortical network in primary visual cortex we analysed how much evidence recent intracellular measurements from cat primary visual cortex (cf. [2]) provide for a particular cortical \"operating point\". Using a Bayesian analysis we find, that the experimental data most strongly support a regime where the local cortical network provides dominant excitatory and inhibitory recurrent inputs (compared to the feedforward drive). Most interestingly, the data supports an operating regime which is close to the border to instability. Hence it is conceivable, that modulatory effects like visual attention may briefly shift the operating point into these regimes, leading to an increased sensitivity of cortical responses to visual inputs.

The presentation is based in part on:

[1] Young J., Waleszczyk W., Wang C., Calford M., Dreher B. and Obermayer

K. (2007), Nat. Neurosci. 10, 887ff [2007].

[2] Marino, Schummers, Lyon, Schwabe, Beck, Wiesing, Obermayer & Sur,

Nature Neurosci. 8, 194ff [2005].

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