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Touring memory lane inside the brain

Say you learn something new, like how to say "thank you" in Russian, or the peak temperature of a hot day on Mars.

The question is: What's really happening inside your brain? What does that memory look like visually, and where in your brain is it taking place?

Stanford Medical School scientists say the video at the top of this post takes them one small step closer to answering that question. Essentially, it's a tour through a thin slice of a mouse's cerebral cortex.

The most interesting sights along the way are individual brain synapses -- the structures that allow brain cells to communicate with one another. In humans, these synapses seem to change throughout our lives as we learn new information.

To get a better look at them, Stephen Smith, a professor of molecular and cellular physiology at Stanford, and his team developed a process called array tomography.

First, they stain the mouse’s brain tissue, so that different kinds of synapses show up in different colors. Then they took thousands of high-definition photos (near the whiskers). Finally, all the images were stitched together into a 3-D video, which can be rotated and “explored.” The scientific nitty-gritty appears in the journal Neuron this week.

The idea, said Smith is that one day, scientists might be able to map the changes in individual synapses that occur when people learn a new skill, or experience pain. The work may also reveal the physical changes that occur in diseases like Alzheimer’s.

That’s a tall order, considering the almost unfathomable complexity of the human brain. Smith says in the human cerebral cortex alone, there are 125 trillion synapses – as many stars as you’d find in 1,500 Milky Way galaxies.

And each synapse is itself like a mini-microprocessor, says Smith, with as many as 1,000 molecular-scale switches. "A single human brain has more switches than all the computers and routers and Internet connections on Earth," he says.

The jaw-dropping complexity of the brain aside, the video is also quite pleasant to look at. Smith said the images "have revealed to me, in a way I wasn’t entirely prepared for, how incredibly beautiful the insides of the brain are." Copyright 2010 KQED Public Broadcasting. To see more, visit

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