A persistent question about [brain] connectomes has to do with what, if anything, distinctive wiring patterns have to do with the evident cognitive differences in a mouse, a monkey or a human.
Hypothetically, the most efficient connectome would follow a one-to-many design, with each nerve cell connecting to all of the others. But this approach is prohibitively unworkable because it requires a lot of space to house all these connections and energy to keep them functioning. Alternatively, a one-to-one design, in which each neuron connects to only a single other neuron would be less challenging—but also less efficient: information would have to traverse enormous numbers of nerve cells like stepping-stones to get from point A to point B.
“Real life is in the middle,” says [researcher] Yaniv Assaf.
Species with few long-range connections linking the two hemispheres of their brain tended to have more short connections within each hemisphere in which nearby areas “talked” intensively with each other. Species with more long-range connections, such as humans and other primates, thinned out these local networks.
This approach to connectivity may reflect geometric constraints on packing a nervous system into a skull. But variations in these links within a species might also track with different abilities. “If you have denser connectivity in one region, you might have a certain ability others wouldn’t,” Assaf says.