 Here’s how to read this diagram: every circle represents a neuron. Associated with each neuron is a certain time—here, the time written beneath that neuron. A neuron can either fire or not fire at its designated time. If the circle is colored grey, this indicates that the neuron fired. If it is colored white, this indicates that the neuron did not fire. So, in the diagram above, b, c, d, and e fired, and a did not fire. Arrows represent stimulatory connections between neurons. If the neuron at the base of an arrow fires, then the neuron at its head will fire so long as that neuron is not inhibited. The circle-headed lines represent inhibitory connections between neurons. If the neuron at the base of one of these connections fires, then the neuron at its head will not fire. So, in the diagram above, a doesn’t fire, even though b did, because c inhibited a.