Yi-Hua Hsu1, 2, Chiao-Chi V. Chen2, Yen-Yu I. Shih3, Chen Chang1, 2
1Institute of Pharmacology, National Yang-Ming University, Taipei, Taiwan, Taiwan; 2Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, Taiwan; 3Research Imaging Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States
Vasoactive neurotransmitters are a direct cause of negative fMRI signals. Dopamine, for instance, can be vasoconstrictive. The dopaminergic system mainly involves a long projection from the substantia nigra to the striatum. The coupling of the fMRI signals with a long vasoactive pathway raises the issue whether the negative fMRI response represents remote rather than local neuronal activity. To clarify, a local anesthetic was used to block the local or remote site of the pathway during induction of the negative fMRI signals. The results indicate that the negative fMRI signals are directly coupled to remote neuronal activation without involving local neurons.