Recent experimental findings show that fast synaptic transmission can extend its actions beyond the immediate synaptic cleft. Whether this phenomenon results in significant crosstalk between typical neighbouring synapses remains unclear. This article considers two areas of the hippocampus, the CA1 and dentate gyrus, where important neural processing occurs. The results discussed do not provide a simple answer to the question of whether synapses can 'talk' to their neighbours, but they do reveal crucial physiological constraints that determine the significance of synaptic crosstalk, thus adding considerably to our understanding of chemical synaptic transmission.