FUNCTIONAL MRI OF PAIN-RELATED AND ATTENTION-RELATED ACTIVATIONS IN THE HUMAN CINGULATE CORTEX

The aims of the study were to use functional magnetic resonance imagin g (fMRI) to 1) locate pain-related regions in the anterior cingulate c ortex (ACC) of normal human subjects and 2) determine whether each sub ject's pain-related activation is congruent with ACC regions involved in attention-demanding cognitive processes. Ten normal subjects underw ent fMRI with a 1.5-T standard commercial MRI scanner. A conventional gradient echo technique was used to obtain data from a single 4-mm sag ittal slice of the left ACC, similar to 3.5 mm from midline. For each subject, interleaved sets of 6 images were obtained during a pain task , an attention-demanding task, and al rest, for a total of 36 images p er task. Pain of different intensities was evoked via electrical stimu lation of the right median nerve. The attention-demanding task consist ed of silent word generation (verbal fluency). Additional experiments obtained data from the right ACC. A pixel-by-pixel statistical analysi s of task versus rest images was used to determine task-related activa ted regions. The pain task resulted in a 1.6-4.0% increase in mean sig nal intensity within a small region of the ACC, The exact location of this activation varied from subject to subject, but was typically in t he posterior part of area 24. The signal intensity changes within this region correlated with pain intensity reported by the subject. The at tention-demanding tasks increased the mean signal intensity by 1.3-3.3 % in a region anterior and/or superior to the pain-related activation in each subject. The activated region was typically larger than the pa in-related activation. Ln some cases this activation was at or superio r to the ACC border, near the supplementary motor area. These regions did not show any pain-intensity-related activation. In one subject bot h right and left ACC were imaged, revealing bilateral ACC activation d uring the attention task but only contralateral pain-related activatio n. These findings shed Light on pain- and attention-related cognitive processes. The results provide evidence for a region in the posterior part of the ACC that is involved in pain and a more anterior region in volved in other attention-demanding cognitive tasks.