Functional Imaging of Neurotransmission

Functional neurotransmitter imaging (fNTI) is an evolving technique that uses molecular imaging to detect neurotransmitters released during a task performance. This technique provides a tool to study neurochemistry of human cognition and involves dynamic measurement of the concentration of a specific radioligand during the task performance. Since ligands are competitively displaced by endogenously released neurotransmitters, a reduction in ligand concentration during task performance indicates task-induced release of endogenous neurotransmitter. Most of the fNTI experiments have used a specific dopamine receptor ligand 11 C-raclopride, which is suitable only for detection of dopamine released in the striatum. Ligands such as 18 F-fallypride and 11 C-FLB456 are potential candidates for detection of extrastriatal dopamine release. Using this technique, we have studied striatal and extrastriatal dopamine neurotransmission during performance of a variety of cognitive and behavioral tasks. These tasks include, motor planning, conscious and nonconscious motor memory, cured-recall, response inhibition and emotional memory. Since, fNTI is an emerging technique, it has so far been used to study only dopaminergic neurotransmission. Its utility in the study of human brain and cognition depends critically on the development of appropriate ligands for other neurotransmitters.