From the Connectome to the Synaptome: An Epic Love Story

Connections by Degree A recent explosion of data and of large projects dealing with the problem of connectivity in the human brain has not yet led to clear strategies to study connectomes. DeFelipe (p. 1198) reviews the intellectual history of the field, from the 19th-century studies of the seminal anatomist Ramon y Cajal to the very recent approaches and myriad new technologies applied by many laboratories trying to understand the organization of the human cerebral cortex. A major challenge in neuroscience is to decipher the structural layout of the brain. The term “connectome” has recently been proposed to refer to the highly organized connection matrix of the human brain. However, defining how information flows through such a complex system represents so difficult a task that it seems unlikely it could be achieved in the near future or, for the most pessimistic, perhaps ever. Circuit diagrams of the nervous system can be considered at different levels, although they are surely impossible to complete at the synaptic level. Nevertheless, advances in our capacity to marry macro- and microscopic data may help establish a realistic statistical model that could describe connectivity at the ultrastructural level, the “synaptome,” giving us cause for optimism.