Comparison of evoked cortical activity in conscious and propofol-anesthetized rats using functional MRI

Changes in cortical activity during foot shock were assessed under consciou s and propofol-anesthetized conditions using functional magnetic resonance imaging (fMRI), Increases in signal intensity were observed in the contrala teral somatosensory cortex in response to electrical shock of the hindpaw u nder bath conditions, These increases in cortical signal ranged from 6% to 26% while awake and from 1% to 6% under propofol anesthesia. In each of the six animals studied, the largest Increase in blood oxygenation level-depen dent (BOLD)-based signal intensity was observed during consciousness. In th ree of six animals, propofol anesthesia depressed signal intensity by as mu ch as 10-fold, showing that the level of cortical activity during foot shoc k is dampened by anesthesia. These results indicate it would be advantageou s to use fully conscious animals to maximize BOLD-based MRI signal in certa in behavioral studies using MR spectrometers with modest field strengths (1 .0-2.0 T). (C) 1999 Wiley-Liss, Inc.