Higher pain rating results in lower variability of somatosensory cortex activation by painful mechanical stimuli: An fMRI study.

Objective: The aim of this study was to find pain-related brain activity which corresponds to self-report pain ratings based on degree of response and repeatability.

Methods: Three painful mechanical stimuli were applied to the right hands of 25 healthy volunteers using monofilaments (forces of 0.98N, 2.94N, and 5.88N). Simultaneously, brain activities were evaluated using functional MRI for a constant stimulus conducted three times in a session. In first assessment, the average percent signal change (PSC) of neuronal response was measured for each region of interest (ROI), secondary repeatability of PSC conducted three times over the session was evaluated for each ROI.

Results: Although the average PSCs for trice stimuli conducted in one session increased in accordance with pain ratings in the somatosensory cortex (S1) and anterior cingulate cortex (ACC), there was a different response between S1 and ACC when subjects rated intense pain; a stable response in S1 against a variable response in ACC.

Conclusions: These results imply that there are different cognitive responses between sensory discrimination and affective component to constant painful stimulus each time.

Significance: Consistency of brain activity based on PSC may be an important biomarker which, along with its neuronal activity, gauges self-report pain ratings.