Final answer:
An fMRI (functional magnetic resonance imaging) is the technique that measures changes in brain oxygen levels over time to track brain activity, offering non-invasive, accurate mapping of brain function during tasks.
Step-by-step explanation:
The method that measures the variations in oxygen located in different areas of the brain over time as a person is doing a task is functional magnetic resonance imaging, or fMRI. This technique tracks the changes in blood flow and oxygen levels in the brain, which in turn indicates activity. When neurons in the brain are active, they consume more oxygen, and since the magnetic properties of hemoglobin change with oxygenation levels, fMRI can detect these changes, allowing for the mapping of brain activity during specific tasks.
Unlike positron emission tomography (PET) scans, which also measure brain activity but with less temporal precision and more exposure to radiation, fMRI provides a non-invasive alternative with better spatial and temporal accuracy. Moreover, fMRI scans are typically preferred over PET scans for brain imaging in modern medical diagnostics and research.