Synaptic boutons, or simply, boutons, are enlargements of the axon, visible with light microscopy, that represent putative synaptic contacts. Bouton density is normally expressed as the number of boutons per 100 μm or per μm.

Each connection between pairs of morphological types could include one or multiple synapses, which in part affects the strength of the connection.

Connection probability is the number of connected pairs among all the tested pairs. Available experimental data suffers from at least two important limitations. First, the data often come from slice experiments where a subset of connections may have been cut. Second, the method usually does not report precise distance of the pairs and this does not allow an accurate replica in the model.

Synapse divergence or outdegree is the number of synapses made by a presynaptic neuron or neuron type.

We can express the synapse divergence also in relation to the postsynaptic target. Here, we calculate the percentage of synapses made by a morphological type onto pyramidal cells or interneurons.

We present here the distribution of synapse divergence per morphological type across the different layers.