Final answer:
Positron Emission Tomography (PET) is the imaging technique that uses radioactive substances to trace neurotransmitter pathways in the brain, allowing for the visualization of physiological activities and blood flow.
Step-by-step explanation:
The neuroimaging technique that uses a radioactive substance to trace neurotransmitter pathways in the brain is Positron Emission Tomography (PET). When performing a PET scan, a mildly radioactive tracer is introduced into the patient's bloodstream, which allows the monitoring of blood flow and physiological activity in different regions of the brain. This is particularly important for identifying active areas of the brain during specific behaviors. Unlike other imaging techniques such as MRI and CT scans, PET scans provide insights into the metabolic processes of targeted organs and can be used to diagnose a range of conditions including brain abnormalities and Alzheimer's disease.