Functional magnetic resonance imaging of the anterior cingulate gyrus and medial prefrontal cortex during visceral and somatosensory pain

The Anterior Cingulate Gyrus (ACG) and Medial Prefrontal Cortex (MPFC) are part of the pain neuromatrix and therefore the multidimensional experience of pain. Although ACG and MPFC activity has been well documented in studies of somatosensory pain, little is known about the activity of these regions during visceral pain. This work uses Blood Oxygen Level Dependent (BOLD) functional Magnetic Resonance Imaging (fMRI) to characterize ACG and MPFC activation and deactivation patterns during visceral pain and draws comparisons with somatosensory pain. It also assesses ACG sub-regional responses to pain and attention tasks and investigates whether ACG sub-regional responses to pain can be modulated by a cognitive distraction task. Comparisons of ACG and MPFC activity during chronic visceral pain revealed a higher percentage of activation in the ACG of control subjects than in patients suffering from chronic visceral pain. Patient and control groups were further differentiated by a deactivation in somatosensory cortex and an MPFC deactivation that bordered on statistical significance. In a comparison of ACG and MPFC activity in visceral and cold pressor pain, midcingulate activity was most prominent during both pain modalities. Lateralization was not significant. ACG and MPFC activity to visceral pain resembled that of left-sided cold pressor pain and both differed from right-sided cold pressor pain. The study on ACG sub-regional modulation demonstrated that distraction from pain results in decreased activation of ACG sub-regions responsive to pain and increased activation in ACG sub-regions responsive to the distraction task. Together, these findings suggest that: (1) ACG and MPFC are key regions in the processing of visceral pain; (2) ACG and MPFC show similar patterns of response in different pain modalities; (3) ACG and MPFC activation patterns may be used to differentiate between health and disease and (4) ACG sub-regional responses depend on the degree of attention directed towards the stimulus.