{"id":147,"date":"2010-12-13T11:41:21","date_gmt":"2010-12-13T11:41:21","guid":{"rendered":"http:\/\/spikingneural.net\/?p=147"},"modified":"2022-11-03T18:08:50","modified_gmt":"2022-11-03T18:08:50","slug":"stable-and-robust-spike-timing-dependant-plasticity","status":"publish","type":"post","link":"https:\/\/blog.spikingneural.net\/?p=147","title":{"rendered":"Stable and robust spike timing dependant plasticity"},"content":{"rendered":"

Im afraid there is more techie maths in this post :(. I recently posted here<\/a> about spike timing dependant plasticity and how it can create unimodal or bimodal synaptic weight distributions depending on whether a term is added to the weight change function to allow dependence on the existing value of the synaptic weight.<\/p>\n

Babadi et al<\/a> show that by adding a delay (d) to the exponential term in additive spike timing depenant plasticity weight change equation (i.e. <\/span>-(|\u0394t|-d) \/ \u03c4) one can stabalize the distribution of synaptic weights to be unimodal instead of bimodal even when no limits are imposed. This is because apparently the relative strength of synapse induces a causal bump near <\/span>\u0394t=0 invoking stronger increases the stronger the weight.This makes sense as the synaptic weight will cause the post-synaptic neuron to fire more quickly and often if it is stronger. This bump can be seen in the image below where on left side of the y axis is the depressive exponential term (though not shown with negative weighting) and on the other side is the potentiating exponential term with the bump:<\/span><\/p>\n

\"\"<\/a><\/p>\n

The delay term makes the causal bump fall into the region where depression occurs.As in the image below (this time the depressive exponential part is shown with its negative weighting):<\/span><\/p>\n

\"\"<\/a>
\n<\/span><\/p>\n

As the synapse gets stronger, a larger portion falls into the depression area, both because the causal bump gets bigger and because it moves closer to <\/span>\u0394t=0. This prevents further growth of the synaptic strength and therefore stops saturation around the bimodal MIN and MAX possible values for synaptic weights.<\/span><\/p>\n

Different studies in synchrony (for a description of synchrony see this post<\/a>) and learning have shown it irrelevant whether excitatory post synaptic potential arrive shortly before or after the post-synaptic spike, but long term depression of synapses occurred when the same synchronous group input was oscillated 180 degrees out of phase so that the excitatory post-synaptic potentials arrived during the troughs of the oscillation, suggesting a certain robustness to the influence of synchronised activity on STDP (read this pdf<\/a> for more info).<\/span><\/p>\n

This finding raises interesting questions as to a possible interplay with a delay term introduced by Babadi <\/span>et al<\/em><\/span>.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

Im afraid there is more techie maths in this post :(. I recently posted here about spike timing dependant plasticity[…]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[29],"_links":{"self":[{"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=\/wp\/v2\/posts\/147"}],"collection":[{"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=147"}],"version-history":[{"count":3,"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=\/wp\/v2\/posts\/147\/revisions"}],"predecessor-version":[{"id":565,"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=\/wp\/v2\/posts\/147\/revisions\/565"}],"wp:attachment":[{"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=147"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=147"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.spikingneural.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=147"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}