Prefrontal cortex activity during resting and task states as measured by functional near-infrared spectroscopy

Liang, Ling-Yin
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University of Delaware
The prefrontal cortex (PFC) is involved in executive functions (EFs) and is important for high-order cognition. Executive functions have been examined by task-induced activation in the PFC. Within neuroimaging results of goal-oriented task study, a consistent task-induced deactivation has been observed in the PFC. The medial PFC shows spontaneous activity during resting states which contributes to the default mode network (DMN). The DMN activates during task-free resting states and deactivates by performing goal-oriented tasks. Functions of the DMN include monitoring environment and processing self-relevant information. The DMN also interacts with high-order cognitive functions and has influences on behavioral performance. The disruption of the DMN could be an underlying mechanism of neurodevelopmental disorders such as autism spectrum disorders (ASD). Structural and functional abnormalities in the PFC have been observed in ASD. In this dissertation, activity in the PFC during resting and task states was examined in children and adults. Measuring brain activity during resting states provides information about the baseline focal activation, which is critical during the interpretation of task-induced activity. The intrinsic property in the brain, regulated by the DMN, can be analyzed as well. In addition, activity in the PFC during an EF task was compared to a simple motor task and a resting state in adults to obtain the model of changes among tasks in a mature system. Then, changes of the PFC activity in children with ASD were compared to typically developed children. Study 1: The activation levels in the PFC during resting states between eyes open and eyes closed conditions were compared in order to provide a rationale for proper baseline selection. A significant higher activation in eyes closed condition compared to eyes open condition suggested eyes open condition may be a better baseline condition for goal-oriented task study. Study 2: Regional differences of activation in the PFC were examined to investigate the relationship between the medial PFC and the lateral PFC. The effect of eyes condition was observed in the left and medial PFC. However, the study failed to identify regional differences in the PFC. Study 3: Activity in the PFC was measured during resting, a simple motor task, and an EF task in adults. A significant higher activity during the EF task was found compared to the resting state. Study 4: Activity in the PFC among 3 conditions was measured in children with ASD and age- and gender-match typically developed children. There was no significant difference in oxygenated hemoglobin and deoxygenated hemoglobin among conditions. There was no interaction of group and conditions on concentration of hemoglobins. However, children with ASD had poor performance of Tower of Hanoi indicated deficits in the PFC. Based on the finding in Study 1, eyes open condition was used as the baseline condition in Studies 3 and 4. When examined the effects of task conditions on the activation, all channels were averaged for comparison since there was no significant difference among regions in the PFC according to the results in Study 2. We found a significant effect of task condition on the activation and the involvement of the PFC during an EF task was verified in Study 3. Due to limited sample size and high variation in our participants, we did not observe a main effect of task condition on the PFC activation in children with and without ASD. Future study needs to focus on participants in specific age ranges in order to explore effects of maturation on EF functions and PFC activity.