The brain has been mapped to the smallest fold for at least a century, but still no one knows how all the parts talk to each other.
A study in Proceedings of the National Academy of Sciences answers that question for a small area of the rat brain and in so doing takes a big step toward revealing the brain's wiring.
The network of brain connections was thought too complex to describe, but molecular biology and computing methods have improved to the point that the National Institutes of Health have announced a $30 million plan to map the human "connectome."
The study shows the power of a new method for tracing brain circuits.
University of Southern California neuroscientists Richard H. Thompson and Larry W. Swanson used the method to trace circuits running through a "hedonic hot spot" related to food enjoyment.
The circuits showed up as patterns of circular loops, suggesting that at least in this part of the rat brain, the wiring diagram looks like a distributed network.
Neuroscientists are split between a traditional view that the brain is organized as a hierarchy, with most regions feeding into the "higher" centers of conscious thought, and a more recent model of the brain as a flat network similar to the Internet.
"We started in one place and looked at the connections. It led into a very complicated series of loops and circuits. It's not an organizational chart. There's no top and bottom to it," Swanson said.
The circuit tracing method allows the study of incoming and outgoing signals from any two brain centers. It was invented and refined by Thompson over eight years.
Most other tracing studies at present focus only on one signal, in one direction, at one location.
"[We] can look at up to four links in a circuit, in the same animal at the same time. That was our technical innovation," Swanson said.
The Internet model would explain the brain's ability to
|Contact: Carl Marziali|
University of Southern California