Mental Fatigue and Functional Near-Infrared Spectroscopy (fNIRS) – Based Assessment of Cognitive Performance After Mild Traumatic Brain Injury

Abstract

Pathological mental fatigue after mild traumatic brain injury (TBI-MF) is characterized by pronounced mental fatigue after cognitive activity. The neurological origin is unknown, and we aimed in the present study to investigate how prolonged mental activity affects cognitive performance and its neural correlates in individuals with TBI-MF. We recruited individuals with TBI-MF ( n = 20) at least 5 months after injury, and age-matched healthy controls ( n = 20). We used functional near-infrared spectroscopy (fNIRS) to assess hemodynamic changes in the frontal cortex. The self-assessed mental energy level was measured with a visual analog scale (VAS) before and after the experimental procedure. A battery of six neuropsychological tests including Stroop–Simon, Symbol Search, Digit Span, Parallel Serial Mental Operation (PaSMO), Sustained Attention and Working Memory test, and Digit Symbol Coding (DSC) were used. The sequence was repeated once after an 8 min sustained-attention test. The test procedure lasted 2½ h. The experimental procedure resulted in a decrease in mental energy in the TBI-MF group, compared to controls (interaction, p < 0.001, η p 2 = 0.331). The TBI-MF group performed at a similar level on both DSC tests, whereas the controls improved their performance in the second session (interaction, p < 0.01, η p 2 = 0.268). During the Stroop–Simon test, the fNIRS event-related response showed no time effect. However, the TBI-MF group exhibited lower oxygenated hemoglobin (oxy-Hb) concentrations in the frontal polar area (FPA), ventrolateral motor cortex, and dorsolateral prefrontal cortex (DLPFC) from the beginning of the test session. A Stroop and Group interaction was found in the left ventrolateral prefrontal cortex showing that the TBI-MF group did have the same oxy-Hb concentration for both congruent and incongruent trials, whereas the controls had more oxy-Hb in the incongruent trial compared to the congruent trial (interaction, p < 0.01, η p 2 = 0.227). In sum these results indicate that individuals with TBI-MF have a reduced ability to recruit the frontal cortex, which is correlated with self-reported mental fatigue. This may result both in deterioration of cognitive function and the experience of a mental fatigue after extended mental activity.

Mental Fatigue after Mild Traumatic Brain Injury in Relation to Cognitive Tests and Brain Imaging Methods

“…However, fatigue in neurological disorders is suggested to be related to circuits that connect the basal ganglia, amygdala, thalamus, and frontal cortex [23]. This is supported by brain imaging studies with TBI participants [24][25][26][27][28][29]. The integration of these areas is important for appropriate behavior and cognitive functioning [30] and also for executive function such as motivation, learning, planning, goal-directed behavior, and emotion regulation [31].…”

Follow-up after 5.5 years of treatment with methylphenidate for mental fatigue and cognitive function after a mild traumatic brain injury

“…Fatigue in neurological disorders has been suggested to be related to circuits that connect basal ganglia, amygdala, the thalamus and frontal cortex (34). Studies of mental fatigue after TBI using functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS) indicate a dysfunction within the cortico-striatal-thalamic circuits (35)(36)(37)(38)(39)(40). These circuits mediate motivation, learning, planning, goal-directed behavior and emotion regulation and the integration of networks is important for appropriate behavior and cognitive functioning (41).…”

Methodologies on the Enhanced Spatial Resolution of Non-Invasive Optical Brain Imaging: A Review

“…These devices enable us to monitor dynamic fluctuations in regional cerebral blood flow (CBF) in real-time by evaluating concentration changes in cerebral hemoglobin [50]- [52]. Different types of cognitive tasks such as motor [53]- [55] and social activity [56]- [58], have been evaluated using NIRS. Currently, fNIRS devices are flourishing and have been noted as being useful in psychiatry [59], [60] and psychology [61]- [64] development.…”