Fig 3. Structural motifs in the network under pair-based and triplet STDP.

A. Examples of structural motifs common for both the pair-based and triplet STDP framework. Here α and β constitute the path lengths of synapses from the source neuron to the postsynaptic neuron i and the presynaptic neuron j. α = 1, β = 0: Presynaptic neuron j projects to the postsynaptic neuron i. α = 0, β = 1: Postsynaptic neuron i projects to the presynaptic neuron j. α = 1, β = 1: Common input from source neuron k to presynaptic neuron j and postsynaptic neuron i. α = 2, β = 0: Presynaptic neuron j projects to the postsynaptic neuron i through another neuron k in the network. B. Illustration of the calculation of the common input motif with α = 1 and β = 1 framed in purple in A (there are also additional terms which are not illustrated). The motif coefficients M_α=1,β=1 (right) are calculated as the total area under the curve resulting from the product of the convolution of the EPSC function E (left) and the STDP functions (pair-based L₂ and triplet L₃, middle). C. Examples of structural motifs found only in the triplet STDP framework, where γ denotes the time-delayed path length from the source neuron to the postsynaptic neuron i. α = 1, γ = 1: Source neuron k projects twice to postsynaptic neuron i with a different time delay. α = 2, γ = 0: Feedback loop through another neuron k in the network (source and projecting neuron are the postsynaptic neuron i). α = 1, β = 1, γ = 1: Source neuron k projects to the presynaptic neuron j and postsynaptic neuron i via all the three possible paths. D. Illustration of the calculation of the motif with α = 1 and γ = 1 for the triplet STDP rule framed in purple in C, compare to B.