APCTP-POSTECH Joint Semina

style=TEXT-JUSTIFY: inter-ideograph; TEXT-ALIGN: justify>size=5>style=FONT-WEIGHT: bold; FONT-SIZE: 18pt; FONT-FAMILY: 맑은 고딕>APCTP-POSTECH
Joint Seminastyle=FONT-SIZE: 10pt; FONT-FAMILY: 맑은 고딕>

style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>*Title :
style=FONT-WEIGHT: bold; FONT-SIZE: 16pt; FONT-FAMILY: 돋움>Cortical Plasticity
and the Cortical "Operating Regime"

style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>*Speaker : Klaus
Obermayer (Bernsteinw:st=on>Center for Computational Neuroscience and w:st=on>Berlinw:st=on>University of
Technology)

style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>*Location : APCTP
style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>세미나실lang=EN-US> (무은재 기념관lang=EN-US> 512호lang=EN-US>)

style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>*Date & Time :
2007.08.31(lang=EN-US>금)
style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>오후lang=EN-US>
3시style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>

style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>*Abstrack

style=FONT-SIZE: 10pt; FONT-FAMILY: 돋움>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.

style=FONT-SIZE: 10pt; FONT-FAMILY: 돋움>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.

style=FONT-SIZE: 10pt; FONT-FAMILY: 돋움>The presentation is based in part
on:

style=FONT-SIZE: 10pt; FONT-FAMILY: 돋움>[1] Young J., Waleszczyk W., Wang C.,
Calford M., Dreher B. and Obermayer

style=FONT-SIZE: 10pt; FONT-FAMILY: 돋움>     K. (2007), Nat. Neurosci. 10,
887ff [2007].

style=FONT-SIZE: 10pt; FONT-FAMILY: 돋움>[2] Marino, Schummers, w:st=on>Lyon, Schwabe, Beck, Wiesing, Obermayer &
Sur,

style=FONT-SIZE: 10pt; FONT-FAMILY: 돋움>     Nature Neurosci. 8, 194ff
[2005].

style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>-style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>주 관lang=EN-US>
: POSTCH NCSL Lab.

style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>-style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>후 원lang=EN-US>
: APCTP, 뇌연구센터lang=EN-US>, 물리학과lang=EN-US>

style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>*style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>문의lang=EN-US>
: 물리학과 김승환 교수lang=EN-US>(☏lang=EN-US>279-8671, href=mailto:swan@postech.ac.kr>swan@postech.ac.kr)

style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: 돋움>뇌연구센터
장나영lang=EN-US> (☏lang=EN-US>279-2961, href=mailto:jny1321@postech.ac.kr>jny1321@postech.ac.krcolor=navy> )color=navy size=2>style=FONT-WEIGHT: bold; FONT-SIZE: 10pt; COLOR: navy>