What we really want to look at in the brain with functional imaging is, you know, brain function. We want to know where neurons are and aren’t firing so we can talk about increased or decreased activity. Trouble is, there’s not an amazing way to measure that directly and finely.
Instead, we can look at indirect markers of activity. Neurons need glucose as fuel, and the brain is notoriously hungry for it. Parts of the brain that are using glucose like crazy are likely firing more than parts that aren’t. In something like a PET scan, the person gets a modified version of glucose with a sort of weakly radioactive tag on it, allowing us to follow it on a scan and see where it’s getting taken up in the brain. In your example, it roughly suggests increased activity in those areas.
More popular in neuroscience research is fMRI, which uses the magnetic change between hemoglobin that does or doesn’t have oxygen attached to gauge how hard groups of neurons are needing oxygen, and indirectly how much they’re firing.
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