214 Chapter 7 Discussion The modified SART is a feasible MRI vigilance task showing similar cinguloopercular, frontoparietal, arousal, visual, and motor-related activity in people with narcolepsy and controls. The same vigilance networks were activated in both groups when analysing the main task and time-on-task effect over repetitions. When comparing activity in the first and second half of the higher difficulty level blocks, people with narcolepsy type 1 had significantly lower activation in the task-positive regions than controls. People with narcolepsy type 1 had significantly lower activation in the left pre- and postcentral cortex when making more errors, than healthy controls. Behavioural effect Participants in both groups reported that the test was straightforward and easy to complete. Only individuals with narcolepsy type 1 made significantly more mistakes when difficulty increased and, in general, reacted more slowly than healthy controls. As well as intrinsic narcolepsy-related complaints resulting in longer response times, those with narcolepsy type 1 probably also sacrificed speed to improve accuracy at moderate vigilance demand (moderate difficulty level). They seemed unable to utilize this trade-off further when vigilance demand increased (higher difficulty level), resulting in an increase in mistakes in people with narcolepsy type 1, whereas healthy controls maintained a relatively stable performance. A similar speed–accuracy compensatory mechanism has previously been proposed by Van Schie et al. [93]. A possible learning effect was only seen when comparing performance during cycle 1 and 4 in the higher difficulty level, suggesting that participants at first were challenged more by the rapid stimulus presentation of the higher difficulty level than the moderate difficulty level. Functional MRI effect Significant “task > baseline” activation was seen in the cingulo-opercular and frontoparietal attention network. Given the relative simplicity of the presented stimuli and the fast pace of stimuli presentation, we propose that task-positive activation of the cingulo-opercular network is related to enabling stable alertness and responsiveness throughout the entire task [286]. A similar role has been proposed for the cingulo-opercular activity as the core of task-set maintenance, related to sustaining attention and handling error processing [287, 288]. The frontoparietal network on the other hand is involved in flexible adaptive control akin to its role in making rapid adjustments after stimulus
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