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In "Behavioral time scale synaptic plasticity underlies CA1 place fields" by Bittner et al. an alternative to Hebbian plasticity is proposed called Behavioral Time-scale Synaptic Plasticity (BTSP). Basically, instead of depending on Hebbian plasticity, a calcium-ion plateau can be used to create associations. From the paper:

BTSP can rapidly store the entire sequence of events that occurred for several seconds before and after plateau-potential initiation within the synaptic weights of area CA1.

However, despite reading the paper, I'm still confused about the mechanism they think performs this. Does the "plateau" cause all spiking neurons to strengthen their connections or does the "plateau" use some other mechanism to influence neurons? Is excitation or potentiation even the correct way to understand this?

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According to the Supplementary Materials the synaptic plasticity rule can be inferred from the data to be:

$$W(z) = W_0(z) + \alpha \sum_{t,t'=0}^{T} R_{CA1}(t')K(t'-t)R_{CA3}(z-x_A(t))$$

Where:

  • $z$ is the preferred location of the place cell
  • $W_0$ is the initial synaptic weight
  • $\alpha$ is a learning-rate constant
  • $T$ is the total running time of the experiment with $t'$ being when the plateau starts, although I'm not sure about $t'$ and it's significance
  • $R_{CA1}$ is a binary function which is 1 in the presence of the plateau
  • $K(t'-t)$ is an unknown kernel that determines synaptic weights change depending on the activity of the cells at time $t'=t$
  • $R_{CA3}(z-x_A(t))$ is a model of the firing rate of the place-cell given the preferred location and the current location of the animal

Given that the formula for weight change depends on both:

  1. The firing rate of the place cell
  2. A kernel which takes the firing rate of the place cell into account

I can say that the plateau selects for firing place cells. However, I'm still not clear on what they mean by storing "entire sequence of events that occurred for several seconds before and after plateau-potential initiation".

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