Fig. 8.

Clustering of synaptic weights uncovers the synfire chain in the reconstructed connectivity matrix. a Connectivity is first clustered by the outgoing connections (columns), while trying to achieve minimal variability inside each group. The dendrogram at the top of the panel shows the hierarchy of the clusters with the relevant groups highlighted in different colors. The green cluster on the left is formed by the inhibitory neurons. The yellow cluster at the right consists of excitatory neurons that are not part of the synfire chain and so do not have strong outgoing connections. The clusters in the middle correspond to the links of the synfire chain, which coalesce as red squares in the matrix. b Clustering by incoming connections (rows) inside the yellow clusterof neurons reveals the last link of the chain. c Clustering by incoming connections inside the green cluster helps to identify the inhibitory neurons that are part of the synfire chain (thin red rectangles)