Fig. 2. Identification of polychronous groups. Schematic of a single polychronous group in three-dimensional model space. Excitatory neurons are shown in green , inhibitory neurons in red. Arrows  connecting neurons indicate the presence of strong synaptic connections. Some neurons connect via  local nonmyelinated axon collaterals, whereas others connect via  long-range myelinated axons (A) . Timeline of the polychronous group depicted in (A)  showing connectivity and axonal delays. Arrows  depict strong synaptic connections. When neurons A, C, and E fire with the timing pattern (0, 7, 11 ms), spikes arrive simultaneously at neuron D. This spiking activity may then propagate along the connected neurons in the group, the membership of which is determined by strong synaptic connections and axonal delays that will allow the coincident arrival of spikes from upstream neurons. When spiking activity is propagated in such a way, this leads to a precise spatiotemporal pattern of firing (B) . Activation of polychronous groups. The upper panel  represents a 3-s time period, displaying the occurrence of action potentials (rectangles) for the subset of neurons in the previously identified polychronous group. The inhibitory neurons, shown in red , fire much more frequently than do excitatory neurons, shown in green . Most of the neuronal firing appears random and uncorrelated. On two occasions during the depicted time period, the majority of the neurons fire in the precise pattern identified in (B) . When the neurons fire in this manner, the polychronous group is said to be activated (C) .