Resting-state functional connectivity, cognition, and fatigue in response to cognitive exertion: a novel study in adolescents with chronic fatigue syndrome.

Emerging evidence suggests that central nervous system dysfunction may underlie the core symptoms of Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) in adults, such as cognitive disturbance, fatigue and post-exertional malaise. Research into brain dysfunction in the pediatric CFS/ME context, however, is severely lacking. It is unclear whether the adolescent CFS/ME brain functions differently compared with healthy peers, particularly in situations where significant mental effort is required. This study used resting-state functional MRI in a novel repeated-measures design to evaluate intrinsic connectivity, cognitive function, and subjective fatigue, before and after a period of cognitive exertion in 48 adolescents (25 CFS/ME, 23 healthy controls). Results revealed little evidence for a differential effect of cognitive exertion in CFS/ME compared with controls. Both groups demonstrated a similar rate of reduced intrinsic functional connectivity within the default mode network (DMN), reduced sustained attentional performance, slower processing speed, and increased subjective fatigue as a result of cognitive exertion. However, CFS/ME adolescents consistently displayed higher subjective fatigue, and controls outperformed the CFS/ME group overall on cognitive measures of processing speed, sustained attention and new learning. No brain-behavior relationships were observed between DMN connectivity, cognitive function, and fatigue over time. These findings suggest that effortful cognitive tasks may elicit similar levels of energy expenditure across all individuals in the form of reduced brain functioning and associated fatigue. However, CFS/ME may confer a lower starting threshold from which to access energy reserves and cognitive resources when cognitive effort is required.