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Visualizing the brain as a Universe of synapses

A new imaging method pioneered by Stanford neuroscientist Stephen Smith, PhD, and his colleagues is set to give the world its best glimpse yet of the Universe that is the brain.

I use the term "Universe" advisedly.

All by itself a human nerve cell, or neuron, is no great shakes. It's pretty much identical to its counterpart in a mouse or a mosquito. The difference lies in the sheer numbers of neurons packed inside the human brain: about 200 billion of them, Smith tells me, each forming up to tens of thousands of specialized contacts called synapses with other neurons near and far. (And neurons are only about 10 percent of all the cells in the brain. The other 90 percent, so-called glial cells, have talents of their own.)

Talk about a network effect.

Only mammals have the brain structure called the cerebral cortex. Scientists believe this six-cell-thick layer coating the brain's surface is largely responsible for our species' intellectual prowess. One single healthy adult's cerebral cortex contains more than 125 trillion - trillion! - synapses. "That's more than the number of stars in 1,500 Milky Way galaxies," says Smith.

Nor are those synapses all alike. They come in a variety of types with differing signaling properties - they're more like microprocessors than mere on/off switches.

"What gets us neuroscientists out of bed in the morning," says Smith, "is our conviction that the brain is ultimately a machine that can be potentially understood." Our intuition fails us, Smith says, because even the most sophisticated machines we can think of are ridiculously simple in comparison to the human brain. Another Stanford brain scientist, Karl Deisseroth, MD, PhD, says the human brain is arguably the most complex entity in the known Universe.

Smith and his team have figured out how to not only accurately and quickly count but also, effectively, color-code synapses by type. And they've translated all that data into a virtual video "fly-through" - in this case, of a mouse's cerebral cortex, which you can watch by clicking on the image above (if you haven't already). KEY: The neurons are long, green, and often branching. The multicolored dots are synapses.

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