A synapse census for the ages

A molecular imaging survey reveals the evolution of mouse brain synapse populations from birth through old age Brains can be viewed as vast ensembles of highly diverse and dynamic synapses that shape and store information as it travels through the networks of neurons that generate and interconnect those synapses. There are more than 100 trillion synapses per human neocortex ( 1 ), and each synapse is itself a highly complex entity, comprising thousands of diverse and cooperative signal-transduction proteins ( 2 ). Growing knowledge of these very large and heterogeneous populations of synapses, or “synaptomes,” thus offers perhaps the most compelling glimpse to date of brains as machines deep and wide enough to support the richness and subtlety of the human mind. On page 270 of this issue, Cizeron et al. ( 3 ) describe the use of a mouse model to begin the task of systematically mapping synaptomes brain-wide, from birth to old age.