Noxious pressure stimulation demonstrates robust, reliable estimates of brain activity and self-reported pain

Figures

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  Fig. 1. Evoked Pressure Paradigm Design. In each block (2 blocks depicted above) participants received a train of three pressure stimuli at either high (noxious; score of 60 determined by thresholding) or low (non-noxious; 55 kPA across all participants) intensity (alternating blocks). Within the train, each pressure stimulus had a total duration of 2 s with an interstimulus interval of 5 s. The first pressure stimulus occurred at a jittered interval after the start of the block (0–1.2 s). Following the train of pressure stimulation, participants were then presented with a computerised VAS of the pain scale. This scale was made up of 100 elements, anchored with 'no pain' at one side (0) and 'worst pain imaginable' (100). This scale was presented for 7 s. This was followed by a jittered interval prior to the start of the next block. There were 20 blocks of stimulation per run (10 noxious and 10 non-noxious blocks). Participants completed two runs in total (left- and right-hand stimulation). Each stimulus (within a train; noxious or non-noxious) contributed to the explanatory variable for either noxious or non-noxious stimulation (block dependant).

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  Fig. 2. Behavioural Data. Left Panel: VAS scores (pain scale made up of 100 elements, anchored with 'no pain' at one side (0) and 'worst pain imaginable' (100)), were higher for noxious stimulation compared to non-noxious stimulation (ANOVA). No other main effects or interactions were significant. Error bars indicate standard error. Right Panel: Plot shows CVs by session and stimulation type (noxious, non-noxious). There was higher dispersion around the mean under non-noxious stimulation compared to noxious stimulation (main effect: ANOVA). No other main effects or interactions were significant.

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  Fig. 3. Evoked Activation for Main Effect of Noxious Pressure Stimulation (Data from Both Hands Incorporated) in Session 1 (Upper Panel) and Session 2 (Lower Panel). In session 1 there were clusters of activation in insula, thalamus and putamen extending into the postcentral gyrus. Additional regions included the cerebellum and primary somatosensory cortices extending into IFG. Peak activation in session 2 followed a similar pattern. Depicted here are two overlays at initial height thresholds p < 0.001 (blue to white), and p < 0.0001 (red to yellow).

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  Fig. 4. Evoked Activation for Noxious > Non-noxious Stimulation (Both Hands) for Session 1 (Upper Panel) and Session 2 (Lower Panel). In session 1 there were significant clusters of activation in regions including bilateral insula extending into the thalamus, putamen, and precentral gyrus. Additional regions included the cerebellum (bilateral) and primary somatosensory cortices. Peak activation in session 2 also centred in the thalamus, primary somatosensory cortices, cerebellar regions and precentral gyrus, and additionally in the IFG, cingulate and supramarginal gyrus. The height threshold was set to p < 0.001.

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  Fig. 5. ICC Distributions. Plots show the relative number of activated voxels against ICC scores for the whole brain and activated network in response to evoked noxious pressure stimulation.

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  Fig. 6. ICC Maps and Significant Clusters for Contrasts of Interest. 6A and 6B depict ICC values [dark blue; 0 to light blue; 1] on upper panels and significant clusters of activation [dark red to yellow, t scores] for contrast on lower panels. 6A. shows main effect of noxious stimulation and 6B. depicts the ICCs and contrast for noxious > non-noxious pressure stimulation.