Authors: Rajendra D. Badgaiyan
Neurotransmitters are important regulators of the brain function. However, their precise roles in the processing of human cognitive and behavioral functions remain unclear primarily due to lack of a technique that allows detection of these neurochemicals during brain processing. Consequently, most of the data concerning roles of neurotransmitters have been acquired in laboratory animals. Since the animal data does not explain many functions of the human brain, we developed a dynamic molecular imaging technique to detect, map, and measure neurotransmitters released acutely in the human brain during processing of a cognitive or behavioral task. The technique exploits the competition between a neurotransmitter and its receptor ligand for occupancy of receptor sites. In these experiments, after volunteers have received an intravenous bolus of a radiolabeled ligand, they are positioned in the positron emission tomography (PET) camera and asked to perform a task. During task performance PET data are acquired dynamically. The concentration measured at the voxel level is analyzed using a receptor kinetic model to estimate values of various receptor kinetic parameters. Based on these values, neurotransmitters released during task performance is detected, mapped and measured. Using this technique we have detected dopamine released in the human brain during processing of a number of cognitive and behavioral tasks. Based on these data we conclude that the technique extends the scope of neuroimaging studies. It can be reliably used to study neurochemical control of human cognition and behavior.
Keywords: PET, dopamine, neurotransmission, raclopride, fallypride, cognition, single scan dynamic molecular imaging