Our discussion of the transmission of activity through synapses concentrated on asynchronous transmission. We defined the ASG as the number of spikes added to the postsynaptic stream after a presynaptic spike, but we were not concerned with the exact time at which these extra spikes were produced. We have shown that if several spikes converge on one postsynaptic target, their effects add up linearly as long as their EPSPs do not overlap in time.

In this chapter we deal with the properties of synchronous transmission of activity. We have already shown that if a cell receives convergent excitations from several sources, their combined effect will be greater than the sum of their isolated effects. Here we examine this property quantitatively. An examination of the properties of synchronous activation of neurons will lead us to the conclusion that diverging/converging chains are bound to transmit activity synchronously.

The last section deals with the question how one can observe synchronous activity experimentally. In fact, this entire book came about because in studies in which we recorded the activity of several neurons simultaneously, we observed phenomena that could be explained only by assuming synchronous transmission through diverging/converging chains.