Connectomics researchers mapping out a wiring diagram for rat brains have found that its structure is organized like the Internet. Scientists have long looked for clues to brain function through its structure focused on biological feature such as the brain’s lobes, grooves and folds.
Now, using this more comprehensive picture of how neurons connect to one another, they’ve discovered local networks of neurons nested into one another like shells.
Corresponding author Larry Swanson, professor at the University of Southern California, Dornsife College of Letters, Arts and Sciences, explains:
“The cerebral cortex is like a mini-Internet. The Internet has countless local area networks that then connect with larger, regional networks and ultimately with the backbone of the Internet. The brain operates in a similar way.”
Two local networks make up the inner shell of the rat’s cerebral cortex. One governs vision and learning, and another taps into bodily concerns like muscle and organ function.
Two other networks, one governing smell, and another that assembles and makes sense of the information from the other three networks, make up the outer shell.
This means that certain flows of information are genetically “hardwired” into the brain, Swanson said.
Brain Connectome Database
The discovery is the result of a huge effort to organize 40 years’ worth of data from peer-reviewed research articles detailing connections in rat brains.
“The data was already out there; it just needed to be compiled into a more useful format,” Swanson said.
Lead author Mihail Bota of USC Dornsife created the database from more than 16,000 reports of connections, which he weighted both on the strength of the connection and the reliability of the methodology used to discover it. The process took more than 4,000 hours to complete. The resulting database is freely available online.
The team used studies of rat brains due to the sheer volume of detailed information available.
Swanson believes that the database can create an important link between human brain studies, which are largely done as non-invasive functional magnetic resonance imaging scans, and rat brain studies, which can be more in-depth.
“Having a wiring diagram for the brain will allow knowledge to flow both ways between human and animal studies,” Swanson said. “This allows us to take theories from human brain scan studies and experimentally verify them in animals, and discoveries made in animal studies are likely to have an analogue in humans.”
Mihail Bota, Olaf Sporns, and Larry W. Swanson.
Architecture of the cerebral cortical association connectome underlying cognition.
PNAS, 2015 DOI: 10.1073/pnas.1504394112
Image: Wellcome Images