Synaptic Learning Plasticity

<p>Apr 21, 2009 7:44 PM

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(from article on dendritic spines in wiki qv.)

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<h2>Plasticity</h2>

<div class="rellink boilerplate seealso">See also: <a href="/wiki/Synaptic_plasticity" title="Synaptic plasticity">Synaptic plasticity</a></div>

<p>As aforementioned, dendritic spines are very "plastic", that is, spines change significantly in shape, volume, and number in small time courses. Because spines have a primarily <a href="/wiki/Actin" title="Actin">actin</a> <a href="/wiki/Cytoskeleton" title="Cytoskeleton">cytoskeleton</a>, they are dynamic, and the majority of spines change their shape within seconds to minutes because of the dynamicity of actin remodelling. Furthermore, spine number is very variable and spines come and go; in a matter of hours, 10-20% of spines can spontaneously appear or disappear on the pyramidal cells of the cerebral cortex, although the larger "mushroom"-shaped spines are the most stable.

Spine maintenance and plasticity is activity-dependent and activity-independent. <a href="/wiki/BDNF" class="mw-redirect" title="BDNF">BDNF</a> partially determines spine levels, and low levels of <a href="/wiki/AMPA_receptor" title="AMPA receptor">AMPA receptor</a> activity is necessary to maintain spine survival, and synaptic activity involving <a href="/wiki/NMDA_receptor" title="NMDA receptor">NMDA receptors</a> encourages spine growth. Furthermore, <a href="/wiki/Two-photon_excitation_microscopy" title="Two-photon excitation microscopy">two-photon laser scanning microscopy</a> and confocal microscopy have shown that spine volume changes depending on the types of stimuli that are presented to a synapse.

Spine plasticity is implicated in <a href="/wiki/Motivation" title="Motivation">motivation</a>, <a href="/wiki/Learning" title="Learning">learning</a>, and <a href="/wiki/Memory" title="Memory">memory</a>. In particular, <a href="/wiki/Long-term_memory" title="Long-term memory">long-term memory</a> is mediated in part by the growth of new dendritic spines (or the enlargement of pre-existing spines) to reinforce a particular neural pathway. By strengthening the connection between two neurons, the ability of the <a href="/wiki/Presynaptic" class="mw-redirect" title="Presynaptic">presynaptic</a> cell to activate the <a href="/wiki/Postsynaptic" class="mw-redirect" title="Postsynaptic">postsynaptic</a> cell is enhanced. This type of synaptic regulation forms the basis of <a href="/wiki/Synaptic_plasticity" title="Synaptic plasticity">synaptic plasticity</a>.</p>