Voxel-based morphometry revealed reductions in grey matter density in pain sensitisers but not in habituaters in pain-modulating brain areas that are impaired in chronic pain.
Previous research in health and disease has shown that exposure to pain changes the density of cortical grey matter (GM). Such structural changes of the brain might, however, depend crucially on how this pain experience is evaluated and processed in the brain. In the present study we aimed to detect pain-rating patterns and underlying GM changes after the application of repetitive painful stimulation using voxel-based morphometry (VBM). Healthy volunteers were investigated (n = 27), receiving 8 noxious and 8 innocuous thermal stimuli on the right forearm for 11 consecutive working days. Data were compared with a control group without any intervention (n = 18). Behavioural data demonstrated that a subgroup of volunteers (n = 14) sensitised, whereas the others (n = 13) habituated over the stimulation days. The VBM analysis revealed no increase but a significant reduction of GM density, eg, in the anterior cingulate cortex, the insular cortex and the frontal cortex, exclusively in the group of sensitisers. By contrast, pain habituaters did not show any density changes in the GM.
Depending on the individual perception of pain during the time course of stimulation, the repetitive application of painful stimuli changed the GM density in pain-processing brain regions exclusively in those subjects who were characterised by the lack of habituation. Because VBM studies investigating patients experiencing chronic pain observed similar decreases in GM density and increasing pain ratings over time, the sensitisers in our study may have a higher vulnerability to developing chronic pain syndromes in later life.