Final answer:
Researchers visualize changes in brain activity using PET scans and fMRI. PET scans track physiological activity with radioactive tracers, whereas fMRI measures brain activity through blood flow and oxygen levels, offering greater detail and temporal precision.
Step-by-step explanation:
The procedures that allow researchers to visualize changes in brain activity over time are PET scans and fMRI. A PET scan uses a radioactive tracer to monitor blood flow and create a map of activity in the brain, which is useful for illustrating physiological functions such as metabolism and blood flow. The fMRI, based on the same principles as MRI, shows brain activity by tracking blood flow and oxygen levels, providing more detailed imagery and better temporal accuracy than PET scans. While PET scans show less detail and are less precise in timing, they are still used in certain contexts, particularly in combination with CT scans, to improve imaging of neurotransmitter receptors.