Fig 5. Second- and third-order cumulants can be described in terms of structural motifs that contribute to weight change.

All motifs up to third order as they arise from the cross-covariance C_ij (top row and Eq 3), the auto-covariance C_ii (middle row and Eq 4) (both C_ij and C_ii together represent the second-order cumulant) or the third-order cumulant K_ij (bottom row and Eq 5). The gray boxes indicate the ‘loop’ motifs. The novel motifs which follow from the triplet STDP rule are those that include the path γ (second and third row).