A Novel Investigation of an In‐Scanner Alternative to the Cold Pressor Test in Healthy Individuals

Figures

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  FIGURE 1. Experimental design. Participants provided their current general perceived levels of pain in a numerical rating scale (NRS) from 0 (‘no pain’) to 100 (‘worst pain imaginable’) following each functional scan. Following the tonic pain scan, participants also provided the average perceived pain during tonic cold stimulation in an NRS. During the tonic pain condition, all participants immersed their right hand in a gelled‐cold water tub. Immediately following fMRI scanning, participants immersed their left hand in a gelled‐cold water tub and provided continuous pain intensity ratings in a visual analogue scale (VAS), consisting of a horizontal line anchored from 0 (‘no pain’) to 100 (‘worst pain imaginable’).

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  FIGURE 2. Summary of behavioural results. (A) ‘Current pain’ NRS scores were significantly higher following the Tonic Pain condition than on the other two. Average NRS scores about perceived pain intensity estimated by participants during the Tonic Pain scan did not differ from average VAS provided outside of the scanner for tonic cold stimulation on the opposite hand. (B) Average continuous VAS ratings for 30‐s bins across 6 min. Error bars represent standard error of the mean (SEM).

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  FIGURE 3. ICA results from components 1–4. Functional networks identified across each condition at group level (green = baseline, red = tonic pain, blue = recovery). First four components were identified by researchers as the ones capturing variability of interest and not artefactual. L = left; R = right.

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  FIGURE 4. Dual regression results. All maps reflect significant extension of group ICA components at alpha 0.05. Sagittal slices displayed at MNI coordinates (from right to left): 62, 50, 36, 22, 8, −6, −20, −34, −48, −62. TFCE = threshold‐free cluster enhancement. MNI = Montreal Neurological Institute. L = left; R = right.

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  FIGURE 5. Seed‐based connectivity results. Significant map depicts decreases in functional connectivity (FC) with the seed (i.e., PAG) during the tonic pain condition compared to baseline. Results are significant following threshold‐free cluster enhancement (TFCE) correction at alpha 0.05. ACC = anterior cingulate cortex; IPS = intraparietal sulcus; L = left; MCC = midcingulate cortex; MNI = Montreal Neurological Institute; R = right.

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  FIGURE 6. DCM results summary. (A) From left to right: Locations of seven nodes comprising the descending pain control pathway used for spDCM analysis. Due to the exploratory nature of the analysis, a fully connected model was initially described. (B) Results from greedy search through nested models; depiction of parametric empirical Bayes (PEB) design matrix, comprising scans from all participants across the three experimental conditions (‘Baseline’, ‘Tonic Pain’ and ‘Recovery’). Matrix columns reflect a group mean, and pairwise comparisons were specified (white colours indicate contrast loads = 1, grey colours indicate contrast loads = 0, black indicates contrast loads = −1). (B) Top row shows a depiction of connections with posterior probabilities greater than 0.75 across each contrast of interest. Off‐diagonal positive numbers (represented by yellow arrows on the corresponding bottom diagram) represent excitatory connections (from locations indicated by rows and to locations indicated by columns), and off‐diagonal negative numbers (represented by blue arrows on the corresponding bottom diagram) represent inhibitory connections. (C) From left to right: Leave‐one‐out cross‐validation…