Pain fMRI Response in Anesthetized Rats Correlates with Behavioral Response to Pain in Awake Rats

Fuqiang Zhao¹, Denise Welsh¹, Mangay Williams¹, Hongyu Annie Liang², Alexandre Coimbra¹, Mark O. Urban², Mark Bowlby², Richard Hargreaves², Jeffrey L. Evelhoch¹, Donald S. Williams¹

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.