Dendritic spine plasticity can stabilize synaptic weights
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1
University of Edinburgh, United Kingdom
Stabilization of synaptic weights is important for long-term memory. Most existing attempts to explain synaptic weight stability assume the existence of elaborate molecular signalling mechanisms. Here we propose a simpler alternative model in which changes in dendritic spines size following plasticity results in stabilization of synaptic strength by modifying local calcium dynamics. Recent experimental studies demonstrate that the size of dendritic spines is increased or decreased following induction of synaptic potentiation or depression respectively (Matsuzaki et al, 2004; Harvey et al, 2008). However, the consequences of altered spine size for signaling events within the spine are not clear. Using a biophysical computer model of a dendritic spine and a common calcium-dependent plasticity rule, we find that different NMDAR conductance to spine-size relationships can result in stable, unstable or even bistable synaptic weight dynamics. When we use parameter estimates from the experimental literature, the model predicts that real spines fall into the ’stable’ category. Our model is sufficient to explain the experimental observations that weak synapses are most susceptible to plasticity protocols and that large spines are the most persistent in vivo. We built reduced versions of our stable and unstable synapses and compared their behavior on a model integrate-and-fire neuron subject to physiological input patterns. We found that the stable synapse model, but not the unstable model, can lead to unimodal synaptic weight distributions similar to those found experimentally. To compare memory storage under the two conditions, we selectively potentiated a subset of synapses, subjected the neuron to ongoing activity and allowed the synapses to follow either the stable or unstable plasticity rules. The stable synapses always retained the memory for a longer period than the unstable synapses. In summary, we propose a biophysical model of how synaptic weights can be stabilized using only known properties of dendritic spine geometry and synaptic receptor distribution. We also investigated the implications of these learning rules for synaptic weight distributions and memory storage. This link can act both as a framework for interpreting experimental data and as a base for future theoretical studies of memory. - Matsuzaki M, Honkura N, Ellis-Davies GCR, and Kasai H. Structural basis of long-term potentiation in single dendritic spines. Nature, 429:761-6 (2004). - Harvey CD, Yasuda R, Zhong H and Svoboda K. The spread of Ras activity triggered by activation of a single dendritic spine. Science, 321: 136-140 (2008).
Conference:
Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010.
Presentation Type:
Poster Presentation
Topic:
Poster session I
Citation:
O`Donnell
C,
Nolan
MF and
Van Rossum
MC
(2010). Dendritic spine plasticity can stabilize synaptic weights.
Front. Neurosci.
Conference Abstract:
Computational and Systems Neuroscience 2010.
doi: 10.3389/conf.fnins.2010.03.00011
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Received:
17 Feb 2010;
Published Online:
17 Feb 2010.
*
Correspondence:
Cian O`Donnell, University of Edinburgh, Edinburgh, United Kingdom, cian@salk.edu