This is my 4th interview with Dr. Seth Grant, the molecular biologist who has discovered surprising things about the evolution of the synapse, including the fact that vertebrates have much more complex synapses than invertebrates.Now his team has developed a method for mapping the synapses across the entire mouse brain. This synaptome reveals surprising diversity depending on which part of the brain is examined. We discuss the implications of this discovery and a new theory of how memory works.