Fuqiang Zhao1, Denise Welsh1, Mangay Williams1, Hongyu Annie Liang2, Alexandre Coimbra1, Mark O. Urban2, Mark Bowlby2, Richard Hargreaves2, Jeffrey L. Evelhoch1, Donald S. Williams1
1Imaging, Merck, West Point, PA, United States; 2Neuroscience, Merck, West Point, PA, United States
Anesthesia is necessary for pain fMRI studies in animals. The relationship between fMRI responses under anesthesia and behavioral responses in awake animals is unknown. The effect of systemic lidocaine on the pain-induced fMRI signals and on the vocalization threshold was compared. While the pain fMRI signal in the primary somatosensory cortex is not altered, pain signals in all other activated regions were suppressed by lidocaine, with the temporal profiles showing a striking similarity to that for lidocaine-caused behavioral responses. Results suggest that 1) pain fMRI results from anesthetized animals are associated with the behavioral response in awake animals and 2) S1 may not be involved in the pain processing.