A schematic diagram of currently established elementary circuit configurations. The red triangle represents the cell body of a pyramidal cell. The thick trunk reaching up and ending with two thinner branches reaching diagonally is the pyramidal cell’s apical dendrite. The branches reaching diagonally down from the triangle’s two lower corners represent its basal dendrites. An axon leaves the bottom center of the pyramidal cell to various destinations (see text). Two other axons (red) enter the diagram. The axon that enters from right comes from other cortical areas. The axon that enters at left from below carries sensory input from the visual thalamus. Two inhibitory interneurons (blue) complete the circuit. ffexc: feed forward excitation, fbexc: feed back excitation, lexc: lateral excitation, ffinh: feed forward inhibition, fbinh: feedback inhibition. Figure 2(A) from “Neocortical Lamination: Insights from Neuron Types and Evolutionary Precursors” published November 7, 2017 in Frontiers in Neuroanatomy.