Does Habituation Affect Conditioned Pain Modulation?

Describing endogenous pain modulation (EPM) phenomena as occurring at “higher” or “lower” neural processing levels may help to better characterize the interactions between these mechanisms. Eleven undergraduate students took part in this experiment designed to assess whether conditioned pain modulation (CPM), a lower-level EPM process in which a painful conditioning stimulus inhibits a less painful test stimulus, can be altered by habituation, a higher-level process. The experiment was composed of three separate sessions. In the first session, participants’ thermal thresholds were determined, they rated the painfulness of the thermal grill illusion, and they rated pain evoked by a CPM-invoking paradigm. In the second session participants were randomly divided into two groups. The habituation group was repeatedly exposed to the conditioning stimulus of the CPM paradigm, painfully cold water. The control group was repeatedly exposed to innocuous water. In the third and final session, thermal thresholds, and painfulness of the thermal grill illusion and CPM-paradigm were reassessed. Results indicated that the expeimental manipulation failed to produce more habituation in the experimental group than the control group. However, data combined across groups displayed a general trend toward habituation for nearly all pain measures in this study, though most were not statistically significant. Nevertheless, there was no trend towards a reduction in CPM in session three, though perhaps this was a reflection of a low sample size. The nature of the habituation observed in this study is theorized, and implications of the independence of CPM and pain habituation are discussed.Bachelor of Scienc