Study design for creating a recalled pain experience based on a preceding nociceptive event.

<p>Each block consisted of a six-second, thermal stimulus, either warm, low pain or high pain. The thermal stimulus was produced by an in-house built thermode which could ramp up to the targeted temperature in 1 second (bell shaped-stimulus for illustration purpose only).For the full duration of the thermal stimulus, a verbal visual stimulus “feeling pain” was shown. This was followed by a delay (time-to-test interval) of eleven seconds during which a fixation cross was presented. Subjects were then instructed by means of a visual stimulus “imagine feeling pain” to recall and imagine the preceding thermal event. This recall was performed in the absence of peripheral somatosensory stimulation. After each recalled pain event, subjects used a visual analogue scale (VAS) to rate the intensity and vividness of the “imagined pain” event. (For further details, refer to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0048711#s2" target="_blank">Materials and Methods</a>.).