Figure 7.

Spinal results. A, Spinal BOLD response to the painful phase of stimulation during the baseline session across all participants. The activation can be most likely attributed to the spinal segment C6. Green line indicates the transverse section (C). B, Enlarged detail of the sagittal depiction (A). C, BOLD responses overlaid on a transversal section of a structural T2*-weighted image. The figure shows that the peak of the BOLD response is located in deeper sections the dorsal horn, ipsilateral to the side of stimulation (left). Color bar represents t values. The visualization threshold is set to p < 0.005 uncorrected. D, The parameter estimates at the peak voxel of the BOLD response to painful stimulation show a comparable BOLD response to the painful phase of stimulation (p) in both groups during the baseline session (s1), but no detectable response for the nonpainful period of thermal stimulation (w). BOLD responses to painful stimulation are strongly reduced during the second experimental session (s2) hindering the uncovering of opioid suspension-related group differences. Error bars indicate SEM. E, However, an MVPA was able to successfully decode the pharmacological condition based on the activity patterns during the second experimental session in a previously identified region in the spinal cord that showed a strong positive BOLD response to painful stimulation (see Results). To investigate the specificity of our findings regarding the involved neuronal pathway, we subsequently conducted a searchlight MVPA across the entire measured volume that likewise compared the spinal activity patterns between the remifentanil and the saline group during the second session. The figure shows spatial coincidence of high predictive values in the accuracy map (red, threshold set to average accuracy > 75%) with the region in the spinal cord that showed a significant BOLD response to painful stimulation (green).