BOLD signal changes induced by thermal stimulation.

(a) Anatomical MR image (top panel) with overlay of respective section from mouse brain atlas (IAL +3.7 mm). Regions relevant for pain processing are indicated (SI: primary somatosensory cortex, forepaw region; MI: primary motor cortex; CGC: cingulated cortex) and representative EPI image (second panel). Combined group activation maps after left and right thermal forepaw stimulation of 45 (n_scans = 19, third panel) and 46°C (n_scans = 12, bottom panel) show activated regions derived from GLM analysis (p = 0.0001, cluster size 15 voxels) for all animals overlaid on the mouse brain atlas. The scale bar indicates the percentage of animals showing significant BOLD activation at the given threshold. (b) Mean temporal BOLD profile of the somatosensory cortex (S1; red with error bars) and thalamus (dashed gray; without error bars) contralateral to the stimulated paw (n_scans = 12, orange). Stimulation parameters: 46°C, 1 mm. Grey shaded blocks indicate stimulation periods. Arrow indicates amplitude measure for quantitative analysis (for somatosensory cortex S1). (c) Maximum BOLD signal amplitude of first stimulation period for S1 and thalamus for T = 45°C/2 mm, T = 46°C/2 mm, and T = 46°C/1 mm. (d) Decay rate of BOLD signal as a function of heat dissipated. There is a linear correlation between the decay rate and the amount of ‘noxious`heat (T_thresh = 42°C, R² = 0.988, open symbols) and (T_thresh = 43°C, R² = 0.974, filled symbols) deposited in the tissue. All values are given as mean ± SEM.