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Additional Brain Areas Involved
Prior to the neuroimaging protocol, participants underwent a single night of ambulatory polysomnography and were instructed to keep a sleep diary each morning for 14 days.
A computer-controlled Medoc Thermal Sensory Analyzer was then used to deliver 4 functional runs, each lasting approximately 5 minutes, and spaced 2 minutes apart.
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Each run included an initial 40-second task-negative period, followed by 3 cycles of alternating 30/60-second task-oriented and task-negative periods, and ended with a 60-second task-negative period. Task-oriented periods consisted of eight 1-second thermal pulses, ranging from warm to painful, delivered under the ball of the right foot.
Functional MRI was used to image brain activity during task-oriented and task-negative periods. To minimize error, researchers used a combination of statistical significance (P ≤ .03) and minimum cluster size (135 µL) to establish the probability of a false positive at 0.0007. The statistical parameter maps were then overlaid on a standardized 3D anatomical volume for localization.
“While in the scanner, they were exposed to a thermal stimulus — a painful heat pulse. However, the analyses focused on task-negative periods — what the brain was doing in between those stimuli — to establish a baseline function of the brain when it is not doing a task,” Dr. Craggs explained.
Results showed that clinically disordered sleep significantly contributed to group differences in areas both inside and outside the DMN, including the right cingulate gyrus, left lentiform nucleus, left anterior cingulate, left superior gyrus, median frontal gyrus, right caudate, and the left inferior parietal lobules.
According to the authors, recruitment of additional brain regions during task-negative periods may signal reorganization of the DMN.
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Although the study did not evaluate treatments, the findings indicate that treating both comorbid conditions may be more effective than treating either one alone, senior investigator Christina McCrae, PhD, chair of the department of health psychology at the University of Missouri School of Health Professions, told Clinical Pain Advisor.
