Scientists have created a detailed, three-dimensional wiring diagram of the mouse brain — the first such diagram for a mammal at such a level of detail.

That should help researchers seek clues about how the human brain works in health and disease.

While it doesn't reveal every connection between each of the rodent's 75 million brain cells, it shows how parts of the brain are connected.

The connectome — essentially a wiring diagram — "provides the most detailed analysis of brain circuitry currently available for any mammalian brain," said neuroscientist David Van Essen of Washington University in St. Louis, co-leader of the human connectome project. "It is truly a landmark study."

The project at Washington University — part of a roughly $40 million five-year effort supported by the National Institutes of Health — is meant to create the first interactive wiring diagram of the living, working human brain.

The new diagram of the mouse brain was described online in the journal Nature by Hongkui Zeng and colleagues at the Allen Institute for Brain Science in Seattle.

The announcement was made one year after President Obama announced a $100 million "BRAIN Initiative" to probe the mysteries of the human brain.

To create the diagram, scientists combined data from more than 1,000 mouse brains, each of which was divided into 140 slices. The diagram revealed some surprises. Zeng said that connections that stay on one side of the brain seem to be always stronger than those that cross hemispheres.

The mouse's neuronal connections also vary widely in strength.

She said, "We think a small number of strong connections and a large number of weak connections may be a fundamental network organization property to allow greater capacity of information processing."

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