How do we safely study living brains? - John Borghi and Elizabeth Waters

521,583 views ・ 2018-04-26

TED-Ed


Please double-click on the English subtitles below to play the video.

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As far as we know,
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there’s only one thing in our solar system sophisticated enough to study itself:
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the human brain.
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But this self-investigation is incredibly challenging;
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a living brain is shielded by a thick skull,
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swaddled in layers of protective tissue,
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and made up of billions of tiny, connected cells.
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That’s why it’s so difficult to isolate, observe, and understand diseases
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like Alzheimer’s.
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So how do we study living brains without harming their owners?
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We can use a trio of techniques called EEG,
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fMRI,
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and PET.
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Each measures something different and has its own strengths and weaknesses,
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and we’ll look at each in turn.
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First is EEG, or electroencephalography,
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which measures electrical activity in your brain.
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As brain cells communicate, they produce waves of electricity.
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Electrodes placed on the skull pick up these waves,
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and differences in the signals detected between electrodes
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provide information about what’s happening.
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This technique was invented almost 100 years ago,
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and it’s still used to diagnose conditions like epilepsy and sleep disorders.
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It’s also used to investigate what areas of the brain are active
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during learning or paying attention.
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EEG is non-invasive,
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relatively inexpensive,
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and fast:
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it can measure changes that occur in just milliseconds.
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Unfortunately, it’s hard to determine
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exactly where any particular pattern originates.
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Electrical signals are generated constantly all over the brain
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and they interact with each other to produce complex patterns.
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Using more electrodes or sophisticated data-processing algorithms can help.
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But in the end, while EEG can tell you precisely when certain activity occurs,
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it can’t tell you precisely where.
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To do that, you’d need another technique,
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such as functional magnetic resonance imaging, or fMRI.
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fMRI measures how quickly oxygen is consumed by brain cells.
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Active areas of the brain use oxygen more quickly.
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So watching an fMRI scan while a person completes cognitive or behavioral tasks
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can provide information about which regions of the brain might be involved.
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That allows us to study everything from how we see faces
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to how we understand what we’re feeling.
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fMRI can pinpoint differences in brain activity to within a few millimeters,
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but it’s thousands of times slower than EEG.
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Using the two techniques together
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can help show when, and where, neural activity is occurring.
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The third, even more precise, technique is called positron emission tomography
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and it measures radioactive elements introduced into the brain.
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That sounds much scarier than it actually is;
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PET scans, like fMRI and EEG, are completely safe.
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During a PET scan, a small amount of radioactive material called a tracer
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is injected into the bloodstream,
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and doctors monitor its circulation through the brain.
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By modifying the tracer to bind to specific molecules,
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researchers can use PET to study the complex chemistry in our brains.
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It’s useful for studying how drugs affect the brain
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and detecting diseases like Alzheimer’s.
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But this technique has the lowest time resolution of all
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because it takes minutes for the tracer to circulate and changes to show up.
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These techniques collectively help doctors and scientists
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connect what happens in the brain with our behavior.
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But they’re also limited by how much we still don't know.
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For example, let's say researchers are interested in studying how memory works.
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After asking 50 participants to memorize a series of images while in MRI scanners,
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the researchers might analyze the results
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and discover a number of active brain regions.
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Making a link between memory and specific parts of the brain
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is an important step forward.
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But future research would be necessary
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to better understand what’s happening in each region,
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how they work together,
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and whether the activity is because of their involvement in memory
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or another process occurring simultaneously.
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More advanced imaging and analysis technology
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might one day provide more accurate results
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and even distinguish
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the activity of individual neurons.
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Until then, our brains will keep measuring, analyzing, and innovating
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in pursuit of that quest to understand
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one of the most remarkable things we’ve ever encountered.
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