Differences in frontal cortical brain function between individuals suffering from pathological mental fatigue following acquired brain injury and healthy individuals.

Pathological mental fatigue (PMF) is a common health concern after acquired brain injuries, with tens of millions affected globally each year. Neuroimaging methods show promising results for establishing associations between PMF and brain function. The aim of this study was to investigate whether and how neural functional activity and connectivity differ during rest and cognitive tasks between people with PMF and healthy controls. Twenty participants suffering from PMF after an acquired brain injury (ABI; stroke or traumatic brain injury) and 19 healthy controls were recruited and underwent cognitive tests and functional near infrared spectroscopy (fNIRS) assessments. The results show that the PMF group and controls exhibited different functional brain activation in the frontal cortex, concerning both neural connectivity and activity. More specifically, the PMF group showed higher Global Efficiency and lower Modularity during resting state and when performing the cognitive tasks Digit Symbol Coding and Symbol Search. The groups also differed in peak oxygenated hemoglobin during the BASE task, with lower oxygenation in the PMF group. In addition, the PMF group was significantly slower than the control group in both neutral and incongruent Stroop trials. However, no group differences were observed in neural activity during the Stroop task, and nor were there differences in reactivity or proactivity as measured using the AX-CPT test. This study has developed the knowledge on the brain correlates of PMF. Future studies should explore the theoretical and practical implications of these results.