Anterior cingulate cortex involving in pain modulation - An functional magnetic resonance imaging study

Objective: To investigate the functional activation patterns of the subregions of anterior cingulate cortex (ACC) in human to electrical stimulation of different intensity with functional Magnetic Resonance Imaging (fMRI) and probe the contribution of this area in pain modulation network. Methods: 10 healthy right-handed volunteers were studied with different electrical intensity stimulation of 1-, 2-, or 3- time pain threshold. The fMRI data were collected by GE signa 1.5T MRI system and postprocessed with software of Analysis of Functional Neuroimages (AFNI) to generate the regional activation maps of ACC, furthermore, the distinctive characteristics of stimulation-BOLD signal in ACC subregions were analyzed according to the fMRI maps from the average of the 10 subjects. Results: The anterior portion of ACC (aACC) showed moderate pain-attention-related activation but not statistically related to the strength of stimulation (average activated pixels of P1, P2, P3 amounted to 324, 429, 562 respectively). The BOLD signal showed a positive linear relation with the increasing stimulation at the dorsal-posterior portion of ACC (average activated pixels of P1, P2, P3 were 311, 964, 1414), which indicated stimulus intensity-dependent responses. The ventral-posterior area of ACC (vpACC) demonstrated pain intensity encoding because the BOLD signal had no significant difference during innocuous condition but displayed remarkable distinction during noxious stimulation in this area (average activated pixels of P1, P2, P3 were 324, 429, 562). Conclusion: Subregions in ACC may play a varied role in the network of pain modulation. Each area of ACC displays segregated activation patterns in response to electrical stimulation with different strength.