Fig. 3. Nano-, micro- and meso-scale process structure supports local and nonlocal connectivity.

a, Matrix of ${\mathbb{C}}^4$ synaptic contacts (pink). Rows/Columns: pre-/post-synaptic cells. 4 zones around the main diagonal delineate growing neighborhoods around each cell with: Zone 0: average immediate neighborhood sizes in ${\mathbb{M}}^4$. Zones 1-3: Zone 0 plus 1, 2 and 3 standard deviations, respectively; Zone 4: remaining ${\mathbb{C}}^4$ contacts not in Zones 0-3. b, 75% of ${\mathbb{C}}^4$ synaptic contacts form locally within Zones 0-2. $n$: empirical count of ${\mathbb{C}}^4$ synaptic contacts. c, Fraction of intra-cluster and intra-zone ${\mathbb{C}}^4$ contacts (total, $n$). Many nonlocal (Zones 3–4) synaptic contacts occur with neurons that traverse different neighborhoods, exhibit flattened protrusions and/or exhibit synaptic compartmentalization. d, Synaptic compartmentalization: RIA synaptic polarity varies with changes in cluster assignment of neighboring cells. White/black arrows label synaptic polarity (inputs/outputs). e-g, Volumetric rendering of selected processes shows local structures that support localized, reproducible synapses. e, RMDV flattened protrusions support synapses onto RMDD, diversifying synaptic polarity. f, RIM protrusions support synapse onto RIB. g, Spine-like extensions (dashed black arrows) from RMEV cell body support synapses from SMBVL (not shown) and SMBVR. All examples observed bilaterally in L4 and adult (Extended Data Fig. 9, additional examples in Supplementary Information 4). Row/Column (a) and cell (d-g) colors denote cluster assignment except e, RMDD (anterior cluster, yellow). Scale bar: 1 μm.