He and colleagues spent the past decade analyzing one cubic millimeter of cerebral cortex (about the volume of a poppy seed) to create the first detailed map of connections in the human brain. | Image courtesy of Jeff LichtmanThey discovered that glial cells, which protect nerve cells, outnumber neurons two to one. Most of the connections in the brain can be characterized as weak—a single synaptic connection from a nerve fiber to a cell. Mapping the whole human brain is not yet possible: the data produced would overwhelm current storage systems. But a basic question that such work would help answer is how the human brain differs from those of other animals.