2.2.5. Experimental procedure

Before the stimulation electrode and the EEG electrodes were set up, the subjects completed the KSS and the PVT test. Ninety electrical stimuli divided in 3 separate blocks of 30 stimuli were given. The stimuli were of three different intensities; 2, 3 and 4 times the individual pain threshold. Each block contained 10 stimuli of all three intensities. Inter-stimulus interval was 10–15 s and inter-block interval was 2 min. Each block had a predetermined random order of which stimulus intensity was given. Subject focused on a marking on the wall to reduce eye movements during EEG-recording. A verbal grading of the pain intensity was given 3–4 s after each stimulus.