Constructing spatial synaptic connectivity for the cortical microcircuit model. (
A) Illustration of pooling of presynaptic cell types. Presynaptic populations
X in the point-neuron model (left box; here

L4E) consist of multiple cell types
x (here

). The layer-specific number of synapses
kyXL (dash-dotted lines) formed between one cell of postsynaptic cell type
y (right part of panel A: morphology projected onto cortical layers 1–6; here
y = p5(L56)) and a presynaptic population
X is given by the sum of all individual cell-type resolved synapse counts
kyxL (dotted or dash-dotted lines). (
B) Bi-directional cell- and layer-specific pooling and dispersing of synapses between presynaptic and postsynaptic cell types. Postsynaptic populations
Y (right box; here
Y = L5E) in the point-neuron model consist of multiple cell types
y (here

). A given presynaptic population
X (left box; here
X = L4E) containing cell types
x (here

) forms cell-type and layer-specific connections within
Y (black connection tree). For the number of synapses
KyXL between population
X and cells of type
y in layer
L (right-most branching of connection tree) the synapse count
KYX between all cells in
X and
Y can be obtained by pooling all synapses onto cell types

and input layers
L. Conversely, for a given total number of synapses
KYX between all cells in
X and
Y, the number of synapses
KyXL onto a specific cell type
y and layer
L can, as described by Equation (), be obtained by calculating the cell-type and layer specificity of connections

and

(see Fig. ) from anatomical data (Table ).