Figure 1
With permission from Huynh et al.24.
Conditioned pain modulation paradigm. Experimental design of the CPM paradigm performed within the MRI scanner. (a) Parallel CPM paradigm was performed with thermal stimuli at the volar forearm and hand. A thermode ramping up to 47.5 °C acted as the TS and two ice bags at 0 °C on the contralateral hand acted as the CS. (b) two randomised CPM conditions were used to assess endogenous pain modulation in each subject. One condition included the application of the genuine CS whilst the other involved the application of two water filled bags at skin temperature (~ 32 °C) which acted as the sham CS. (c, d) Each condition consisted of eight TS applied to the dominant volar forearm which started with a waiting period of 15 s followed by the TS that lasted 10 s. Following each TS, a 20 s period was allocated to obtain the pain perception of TS and CS on an NRS. The inter-stimulus interval between each TS was 35 s. CPM, conditioned pain modulation; CS, conditioning stimulus; MRI, magnetic resonance imaging; TS, test stimulus.
