While many areas in the brain are known to correlate with the sensation of pain, the processes that produce fatigue are much less understood. At the IACFS meeting, Yasuyoski Watanabe, M.D., of Japan, described his work to identify the “fatigue centers” in the brain using positron emission tomography (PET), an imaging technique that measures brain blood flow. A reduction of blood flow in any brain region represents a drop in metabolic activity and a depletion of the energy supply in that region. Watanabe evaluated what happened in the brains of healthy subjects undergoing ten consecutive sessions of mental tasks that lasted two hours. A total of ten PET scans were taken during the two-hour series of testing and, after each one, the subjects rated their level of perceived fatigue on a scale from 0 to 100. As anticipated, each consecutive test led to the subject’s increase in fatigue scores and by the last test, most of the 12 subjects rated their fatigue close to 100. In other words, their cognitive abilities were zapped.
As the fatigue ratings of the subjects increased, Watanabe noticed a significant drop in blood flow to two important areas in the prefrontal and frontal cortex. He says that these areas are involved in motivation, sensory evaluation, and the process of habituation to a new environment. Summing up the study findings, Watanabe says, “These two parts of the brain are related to our fatigue sensation.”
The foregoing study was done in twelve healthy volunteers. What about the PET findings in patients with CFS? PET studies indicate that additional areas within the anterior cingulate cortex (ACC) have reduced blood flow in the brains of people with CFS. Watanabe pointed out that the ACC contains important pain processing areas that use the neurotransmitter, serotonin, to combat pain. Using a tracer to measure the serotonin content in the ACC, he found that the lower the serotonin level, the greater the CFS patient’s pain. The close proximity of the pain and fatigue centers in the ACC could explain the high pain levels in many CFS-diagnosed patients and the overlap between FMS and CFS.
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