There are two basic modes of communication used between neurones in thenervous system: neurotransmission and neuromodulation. When representations ofneural circuits are drawn, they tend to include only fast neurotransmission.This can lead us to believe that neurotransmission conveys information throughthe nervous system and that neuromodulation merely modifies theneurotransmission. Even the words that we use to describe these two forms ofcommunication imply that meaning. However, the very act of modifyingneurotransmission conveys information. Therefore, in order to better understandinformation flow in the nervous system, we need to determine howneuromodulation is integrated into neuronal circuits.