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[mellow music]

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<v Narrator>View all the details of the brain,</v>

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researchers need to slice it into thin sections.

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They start by fixing the brain in formaldehyde.

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Then sugar is added to protect

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the delicate tissue during freezing.

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The brain is then frozen into a block of soft material.

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A machine cuts the block into thin slices.

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Even though the process is mechanized,

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you still need a person to move each slice into storage.

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The high-tech equipment they use to move it?

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A paintbrush.

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By keeping track of the slices, the 3D structure

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of the brain is preserved as an ordered stack of sections.

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Unfortunately, the slices come off the machine

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as a bit of a crumpled mess.

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Again, human intervention is required to sort them out.

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Each slice has to be floated in water so that it unfurls,

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with little help from another paintbrush.

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Once unfurled, it's placed on a glass slide

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that it sticks to, allowing it to be lifted from the water.

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To see the individual nerve cells,

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researches rely on a series of stains.

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One colors cell bodies, another the nerve fibers, and so on.

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Each stain is applied to the slides,

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then excess is rinsed off.

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By the time the process is done,

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the brain is ready to be imaged at high magnification.