Figure 1.
Study design for creating a recalled pain experience based on a preceding nociceptive event.
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 Materials and Methods.).
Table 1.
Neural activation during recalled pain.
Table 2.
Comparing recalled pain (high pain) and recalled warm conditions.
Figure 2.
Nociceptive specific activity in the posterior insula.
A) Neural activity specific to processing physical pain (high physical pain > recalled high pain). Group contrast, mixed effects, Z = 2.3; p = 0.01, see Table 3 for further details of coordinates. B) Group mean parameter estimates of peak activity during physical and recalled pain describing observed nociceptive specific activation of posterior insula as compared to anterior insula. Error bars represent standard error. C) Timecourse analysis of posterior and anterior insula showing mean signal change across “Feeling pain” and “Imagine feeling pain” events. Insets shows results of (top) posterior insula activity from a contrast of high physical pain > recalled high pain (see Table 3) and (bottom) anterior insula activity as revealed by a conjunction analysis of common activity across the physical and recalled high pain conditions (see Table 5 for further details of coordinates). Error bars represent standard error.
Table 3.
Group contrast (mixed effects) comparing high physical pain and recalled high pain conditions.
Table 4.
Neural activity specific to perceiving a physical painful stimulus.
Table 5.
Group contrast (mixed effects) conjunction analysis.
Figure 3.
A) Linking nociceptive intensity and therefore posterior insula activity during physical pain with neural activation during subsequent recall. Left: graphical summary of group mean parameter estimates (PE) of percent signal change in posterior insula during high physical pain. Error bars represent standard error. Right: predicted activity during recalled high pain incorporating individual PEs as a regressor. See Table 6 for further details of MNI coordinates. B) Intensity coding during recalled pain. Left: graphical summary of recalled intensity ratings across conditions of imagined stimuli. Error bars represent standard error. Right: Brain regions from a whole brain search whose activity increases with increased perceived intensity of the imagined stimulus and are not seen in the similar analysis performed to explore vividness encoding. Group contrast, mixed effects, Z = 2.3; p = 0.01. See Table 7a for full list of activation with MNI coordinates.
Table 6.
Activation during recalled pain predicted by posterior insula activation during physical pain.
Table 7.
Function fitting analysis.