A) Unprocessed, non-colorized T1-weighted MR image from one animal demonstrating detailed anatomy. ROIs are depicted in red and were used to determine voxel intensities for the lateral muscle (splenius, lower lateral ROI) and dorsal muscle (cleidomastoid, upper midline ROI) regions. B.) ROI mean voxel intensity in the lateral muscle region expressed as percent change from baseline scans showed neither a significant main effect of dose nor time following injection of MnCl2 (p>0.05, for both). C) ROI mean voxel intensity in the dorsal muscle region expressed as percent change from baseline scans following i.p. injection of MnCl2 showed a significant effect of time (*, p<0.05, main effect of time) but showed no significant effect of dose (p>0.05, main effect of dose).