A collaborative study by researchers in Spain and the U.K. found that CFS patients do not engage the working memory of the brain in the same way as healthy control subjects do. The results were published in the peer-reviewed journal Psychosomatic Medicine.
Working memory refers to the capacity to store information in short-term registers while simultaneously manipulating it to perform a task. This is a crucial cognitive function for human thought processes such as reasoning and comprehension because it enables us to process task-relevant information.
Using fMRI imaging on the brain, 17 patients with CFS and 12 healthy control subjects were scanned while performing a specific set of increasingly challenging memory tests. Study participants were presented with a series of capital letters projected onto a screen, one at a time. As this occurred participants were required to press a button whenever the letter presented was the same as one presented a specified number of images previously—first at 1 image previously, then at 2 and finally at 3 images previously (1-back, 2-back and 3-back). This is called an n-back test.
Both groups performed comparably well and activated the working memory network during all task levels. However, during the “1-back” test session, the fMRI showed that patients with CFS experienced greater activation in the medial prefrontal regions of the brain. Furthermore, on the “2- and 3-back” sessions, patients, but not control subjects, significantly activated a large cluster in the right inferior/medial temporal cortex. In fact, trend analyses of task load demonstrated statistically significant differences in brain activation between the two groups as the demands of the task increased.
These results suggest that patients with CFS show both quantitative and qualitative differences in activation of the working memory network compared with healthy control subjects. The researchers leading this study speculate that patients with CFS may recruit alternate regions of the brain to compensate for problems in the working memory network.
Casera X, Mataix-Cols D, Giampietro V, Rimes K, Brammer M, Zelaya F, Chalder T, Godfrey E. Probing the working memory system in chronic fatigue syndrome: a functional magnetic resonance imaging study using the n-back task. Psychosomatic Medicine 2006; 68:[e-published ahead of print]