Shedding light on cognitive control

Sammanfattning: This thesis aimed to investigate the ability to adjust cognitive processes and behavior, i.e., cognitive control, and its related functional activity in the cortex. The optical imaging technique functional near-infrared spec- troscopy (fNIRS) was used to detect change in cortical activity during neu- ropsychological tests of conflict processing and proactive cognitive control The two first studies used a test-retest design and investigated how pro- longed mental activity, neuropsychological testing for two and a half hours, affects cognitive performance and functional activity in the frontal cortex in individuals suffering from pathological mental fatigue after trau- matic brain injury (paper I) and exhaustion disorder (paper II). We were able to show that both patient groups have reduced functional activity dur- ing cognitive control, especially in the left ventrolateral prefrontal cortex, and that this reduction was associated with the level of pathological mental fatigue. There was no indication that prolonged mental activity induced a change in functional activity during the test session. Paper III showed that increased trait mental fatigue in healthy adults was associated with a tendency to use cognitive control in a reactive way. The increase in trait mental fatigue was also associated with an increased func- tional activity in frontal and parietal cortex during reactive conflict pro- cessing situations compared to proactive ones. In the last studies, we brought the fNIRS machine to two schools to inves- tigate functional brain activation during mathematical cognition (paper IV) and cognitive control (paper V) in children between the age of 8- to 9- years in a school environment. The result suggested that the visual aid in mathematical tasks reduces the cognitive load and the functional activity in the right anterior dorsolateral prefrontal cortex, compared to equivalent tasks without visual aid. Children who tend to be less reactive or more pro- active in a conflict processing test involve the right posterior parietal cortex more during reactive situations than proactive ones.