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Jimbo, Tateno, and Robinson did a network plasticity experiment using cultured networks and a MultiElectrodeArray.
They determine the effect of a tetanus at one electrode in a network on the network. Specifically, they look at how the tetanus potentiates or depresses the ability of a test pulse at another electrode to evoke spike trains at various neurons across the network.
They grew cultures on a MultiElectrodeArray for a month. They stimulated each electrode in succession with a test pulse. They recorded the response at all electrodes after each test pulse. They used SpikeSorting to identify the reponses of individual neurons out of the electrode traces. They found that the network’s response to a given test pulse was reproducable for about 50ms after the test pulse.
Then they applied a strong stimulus (a tetanus) to a single electrode (to make it learn :) ). After that they re-characterized the network’s responses to test pulses at every site.
They found that some electrode sites became more potent (“potentiated response”) after the tetanus was applied. This means that, when a test pulse was applied to this electrode site, neurons in all areas of the network responded either the same, or more strongly than they had before the tetanus.
Other sites became less potent (“depressed response”) after the tetanus was applied.
Surprisingly, it was very rare for any given electrode site to become better at stimulating some neurons and worse at stimulating others as a result of the tetanus.
Averaged over trials, about 34% of the electrode sites showed potentiated responses and about 9% showed depressed responses1.
What determined which electrode sites became potentiated and which ones became depressed? The tetanus potentiated electrodes which evoked spike trains that tended to contain spikes which were within 40ms of the spike trains evoked by the tetanus electrode, and depressed others2 . That is, it potentiated sites which evoked patterns similar to the patterns evoked by the tetanus site.
However, the spike trains evoked by both potentiated and depressed neurons became more synchronized with the tetanus electrode after applying the tetanus.
Or, as the paper put it, the tetanus is “enhancing the frequency of spikes that coincide closely with spikes in the tetanized pathway3 and depressing the frequency of those that do not …. tetanic stimulation caused a relative strengthening of the parts of each stimulus pathway that are closest in correlation to the tetanus-activated pathway and depression of the rest. If the stimulus-activated pathway is initially closely correlated in time, then an overall enhancement of firing is produced, whereas if it is loosely correlated, a depression in overall number of spikes results.” 4
See page 5 of Potter (2001) for another review of this work.
Footnotes:
1. actually I’m not too sure about this; the paper actually used SpikeSorting to look at the responses of single neurons, not just electrodes; I couldn’t find the number 6 (out of 64 site; that’s where I got 9%) in the paper, but I saw it in another paper (Potter (2001)) that reviewed this paper
2. In more detail: they calculated the cross-correlation of activity evoked in a given neuron by a test pulse at the tetanus electrode with activity evoked in that same neuron by a test pulse at a given electrode site. They summed this over all neurons in the network. They found that the amplitude of cross-correlation within a 40ms window determined if the given electrode site was potentiated or depressed.
3. they use the term “pathway” to mean what I called “electrode site”
4. Another way of putting this: Consider a neuron N. Consider the spike train SA evoked at N by a test pulse at electrode A, and also the spike train SB evoked at N by a test pulse at electrode B.
Now, stimulate at electrode B with a tetanus. Now if you give a test pulse at electrode A, you’ll find a different evoked spike train, SA’. How can you describe the effect of a tetanus at B on the spike train evoked at N by a pulse at A?
JimboTatenoRobinson99 says that the tetanus will alter this evoked spike train in such a way as to increase the amount of spikes which occur within 40ms of spikes evoked by the tetanus electrode, and to reduce other evoked spikes. That is, start with SA. In order to get SA’, you increase the probability of spikes which are within 40ms of a spike in SB, and decrease the probability of other spikes.