New research suggests that the brain has an interconnected network much like the Internet.

Larry Swanson and Richard Thompson from the University of Southern California in Los Angeles isolated a small section of a rat’s brain in the nucleus accumbens, which is a brain region associated with pleasure and reward.

The scientists used a technique that hinges on the injection of “tracers” at precise points in the brain tissue.  These are molecules that do not interfere with the movement of signals across the tissue, but can be illuminated and identified when using a microscope.

The researchers used this technique to inject two tracers at the same point at the same time.  One tracer showed where signals were going and the other showed where they were coming from.  The approach shows up to four levels of connection.

The researchers saw loops between different regions, feeding back to and directly linking regions that were not known to communicate with one another.  This model is compared with the way the Internet works.
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Scientists originally thought that the brain has a hierarchical structure like a large company.  The “to” and “from” diagram would show straight lines from independent regions up towards a central processing unit.

The new research shows that the region of the brain studied by the scientists displays a network connecting regions associated with stress, appetite and depression.

A highly interconnected structure could prove to be a powerful tool in analyzing how the brain processes information.  This structure had been hypothesized for a long time, but had not been demonstrated experimentally until now.

“You would be amazed at how much of the current experimental neuroscience literature is dominated by ‘top down-bottom up thinking’, which goes back to the 19th Century, especially in neurology,” Professor Swanson told BBC News.

“The bottom line is that no matter what you might think, the circuitry we’ve shown – that specific set of structural connections – has not been demonstrated before.”

The work highlights just one tiny corner of the vast number of connections in a small mammal’s brain.  However, a great picture could emerge by slightly overlapping one mapped region with another.

“This method is repeatable in a sensible way so that neural networks can be followed as far as they go – ultimately to the whole wiring diagram of the brain,” Swanson said.

A diagram like this would be boundlessly complex, and the degree to which it could shed light on the more slippery questions of consciousness and cognition is still uncertain.

“We have no idea right now, but the direct analogy is with the Human Genome Project: taking on faith that knowing the complete sequence of human DNA would be a foundation stone for biology, no matter how long the understanding may take to realize in practical terms.”

The research, which was published in Proceedings of the National Academy of Sciences, may lead to a full map of the nervous system.