Brain Physiology, Cognition and Consciousness: topic
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Metaplasticity: any relation with consciousness?
Alfredo Pereira Jr
Tuesday, 22 January 2008 12:20 UTC
Dear All:
MIT researcher Mark Bear and collaborators have done research and written interesting papers on metaplasticity (see recent Abstract below). Perceptual consciousness seems to be involved in this phenomenon – but how?
I would like to know you opinion.
This research also clarifies the possible role of NMDA different subunits in learning/memory/plasticity and possibly in conscious perception.
Best Regards,
Alfredo
Neuron. 2007 Feb 15;53(4):495-502.
Obligatory Role of NR2A for Metaplasticity in Visual Cortex.
Philpot BD, Cho KK, Bear MF.
Light deprivation lowers the threshold for long-term depression (LTD) and
long-term potentiation (LTP) in visual cortex by a process termed metaplasticity,
but the mechanism is unknown. The decreased LTD/P threshold correlates with a
decrease in the ratio of NR2A to NR2B subunits of cortical NMDA receptors
(NMDARs) and a slowing of NMDAR-mediated excitatory postsynaptic currents
(EPSCs). However, whether and how changes in NR2 subunit expression contribute to
LTD and LTP have been controversial. In the present study, we used an NR2A
knockout (KO) mouse to examine the role of this subunit in the
experience-dependent modulation of NMDAR properties, LTD, and LTP. We found that
deletion of NR2A abrogates the effects of visual experience on NMDAR EPSCs and
prevents metaplasticity of LTP and LTD. These data support the hypothesis that
experience-dependent changes in NR2A/B are functionally significant and yield a
mechanism for an adjustable synaptic modification threshold in visual cortex.
PMID: 17296552 [PubMed – in process]
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Replies
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An evidence for a cognitive role of LTD (Abstract below) – Alfredo
Neuron. 2008 Apr 24;58(2):186-94.
Expression of long-term depression underlies visual recognition memory.
Griffiths S, Scott H, Glover C, Bienemann A, Ghorbel MT, Uney J, Brown MW,
Warburton EC, Bashir ZI.MRC Centre for Synaptic Plasticity, Department of Anatomy, University of Bristol,
Bristol BS8 1TD, UK.The modifications occurring in the brain during learning and memory are still
poorly understood but may involve long-lasting changes in synaptic transmission
(synaptic plasticity). In perirhinal cortex, a lasting decrement in neuronal
responsiveness is associated with visual familiarity discrimination, leading to
the hypothesis that long-term depression (LTD)-like synaptic plasticity may
underlie recognition memory. LTD relies on internalization of AMPA receptors
(AMPARs) through interaction between their GluR2 subunits and AP2, the clathrin
adaptor protein required for endocytosis. We demonstrate that a peptide that
blocks interactions between GluR2 and AP2 blocks LTD in perirhinal cortex in
vitro. Viral transduction of this peptide in perirhinal cortex produced striking
deficits in visual recognition memory. Furthermore, there was a deficit of LTD in
perirhinal cortex slices from virally transduced, recognition memory-deficient
animals. These results suggest that internalization of AMPA receptors, a process
critical for the expression of LTD in perirhinal cortex, underlies visual
recognition memory.PMID: 18439404 [PubMed – in process]
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