| dc.description.abstract | Objectives: The goal of this thesis was to examine the neurocognitive mechanisms of mental workload for the purpose of improving our knowledge of the long-term effects of concussion. Four experiments were performed manipulating mental workload in individuals with and without a history of concussion. Studies one and two increased mental workload by manipulating set size (i.e., number of items to be remembered) and task condition (single-task, dual-task) in individuals with and without a history of concussion, respectively. In addition, event-related potentials (ERPs) were recorded to examine the neural correlates of information processing that are affected by mental workload. Study three examined mental workload by changing the requirements of the task through the manipulation of pattern configuration characteristics. The fourth study examined mental workload in individuals with and without a history of concussion using three types of workload manipulation: set size, task condition, and pattern configuration complexity.
Methods: Thirty-six participants (20 no-concussion, 16 asymptomatic) were recruited for studies one and two, and assessed using a dual-task paradigm involving a computerised eCorsi block task and auditory oddball task that progressively increased in workload (i.e., set size, task condition). ERPs were used to study the sensory and cognitive stages of information processing as a function of mental workload. Seventeen participants (14 no-concussion, 3 asymptomatic) were tested in study three using a computer and phone version of the eCorsi task, which manipulated workload by changing the average angle of a patterns at set sizes of five to eight blocks. Study four examined secondary auditory oddball performance as a function of eCorsi pattern complexity in nineteen participants (9 no-concussion, 10 asymptomatic).
Results: The no concussion group showed reduced eCorsi recall accuracy as set size increased, which was maintained between task conditions (single, dual). In contrast, auditory oddball performance decreased (i.e., poorer accuracy, longer response times [RTs]) as mental workload increased (task, set size). ERP’s showed amplitude reductions in early sensory (P50) and later cognitive (P300) potentials when both tasks were performed simultaneously compared to alone. In contrast, later sensory (N100) ERP increased in amplitude. Sensory gating was consistent at both P50 and N100 potentials as a function of mental workload. The concussion history group showed poorer auditory (lower accuracy, more errors of commission, and longer RTs) when both tasks were performed simultaneously whereas no between-group differences were found on the eCorsi task. ERPs indicated poorer sensory gating (P50, N100) and cognitive processing (i.e., reduced P300 amplitude) in the asymptomatic group, which changed as a function of workload. Investigating the properties of the dual-task showed reduced eCorsi recall accuracy in hard patterns (smaller angles, more crosses, and longer distances) compared to easy patterns; however, this did not affect auditory oddball measures.
Conclusions: Sensory and cognitive processes change as a function of mental workload (task, set size) and in those with a history of concussion suggesting these individuals have problems gating in important information, which may affect the efficiency of later cognitive processes and subsequent behavioural performance. Importantly, mental workload can be increased by task condition (single, dual), set size (# of items to remember), and path configuration difficulty (easy, hard), which reflect different types of load. These findings are particularly useful in the development of sensitive neurocognitive tests for identifying persisting deficits in individuals with a history of concussion. | en |
