Abnormal structure and functional connectivity of the anterior insula at pain-free periovulation is associated with perceived pain during menstruation.

Neuroimaging studies have demonstrated the critical role of the insula in pain pathways and its close relation with the perceived intensity of nociceptive stimuli. We aimed to identify the structural and functional characteristics of the insula during periovulatory phase in women with primary dysmenorrhea (PDM), and further investigate its association with the intensity of perceived pain during menstruation. Optimized voxel-based morphometry and functional connectivity (FC) analyses were applied by using 3-dimensional T1-weighted and resting functional magnetic resonance imaging (fMRI) in 36 patients at the peri-ovulation phase and 29 age-, education-, and gender-matched healthy controls (HC). A visual analogue scale (VAS) was used to examine the intensity of the abdominal pain at periovulation and menstruation. In our results, PDM patients had significant higher VAS-rating during menstruaion than periovulation. Compared with the HC, PDM patients had lower gray matter density in the left anterior insula (aINS). Taken the left aINS as a seed region, we further found hypoconnectivity between aINS and medial prefrontal cortex (mPFC), which showed negative relation with the VAS during menstruation. As the aINS is a key site of the salience network (SN) and the mPFC is a critical region in the default mode network (DMN), it's implicated a trait-related central-alteration that communications between pain attention and perception networks were disrupted without the ongoing menstrual pain. Moreover, result of correlation analysis, at least in part, suggested a possible role of altered FC (pain-free period) in predicting pain perception (menstruation).