In patients with chronic pain, rumination—repetitive focus on discomfort—is linked to altered functional connectivity in the brain's default mode network. In a study of 17 patients with temporomandibular disorder and 17 matched healthy controls, those with chronic pain showed enhanced connectivity between the medial prefrontal cortex and other default mode network regions, including the posterior cingulate cortex and precuneus. Among patients, greater rumination about pain correlated with stronger connectivity between the medial prefrontal cortex and the posterior cingulate cortex, precuneus, retrosplenial cortex, medial thalamus, and periaqueductal gray. These results suggest that communication within the default mode network and with the descending pain modulatory system underlies the degree of rumination about chronic pain.
Daydreaming is linked to how brain networks fluctuate over time, not just their average connectivity. In healthy adults, those who daydreamed more showed less stable connectivity between the posterior cingulate cortex and a part of the default mode network involved in future thinking. However, greater moment-to-moment variability in that same network's connectivity predicted more mind-wandering during a sensory task. The findings suggest that dynamic, rather than static, brain network activity reflects the conscious experience of daydreaming.
In people with neuropathic pain, white matter structure in the default mode network and a pathway connecting the medial prefrontal cortex to the periaqueductal gray is linked to how much ketamine reduces central sensitization, a key pain mechanism. Among 35 patients treated with ketamine, pretreatment fiber density in the anterior limb of the internal capsule correlated with pain relief (r = 0.48), and fiber density in the default mode network (r = 0.52) and the medial prefrontal cortex-periaqueductal gray pathway (r = 0.42) correlated with reduced temporal summation of pain, a marker of central sensitization. However, white matter structure did not distinguish responders from nonresponders.