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How does a functional magnetic resonance imaging (fMRI) scan the brain?

The functional magnetic resonance imaging (fMRI) scan is founded on the notion that blood that is carrying oxygen from the lungs behaves differently - in a magnetic field - than blood which has released its oxygen to the cells.

In other words, the magnetic resonance is different for oxygen-rich blood than it is for oxygen-poor blood.

Since the more active areas of the brain receive more oxygenated blood, the fMRI is able to pick up this increased blood flow and pinpoint where greater activity is occurring.

The measure of the blood volume, blood flow and oxygen use is described as the blood-oxygen-level-dependent signal, or BOLD for short.

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