Intelligence, Task Difficulty, and the Regulation of Activity in the Brain’s Default Mode Network

This study investigates intelligence-related differences in the adjustment of brain activity and connectivity to varying cognitive demands, testing for a moderation of an association between intelligence and neural efficiency by task difficulty. In 72 young adults (34 female, 38 male), fMRI brain activity changes during a decision-making task with five levels of difficulty were related to intelligence scores from a non-verbal matrix reasoning test. In fronto-parietal, subcortical, and cerebellar regions activated during task processing, we observed smaller increases in brain activity in more intelligent participants – independent of task difficulty. However, in two regions of the default mode network, dorsomedial prefrontal cortex (DMPFC) and left angular gyrus (AG), more intelligent participants showed greater decreases in activity with increasing task difficulty. Furthermore, with increasing difficulty, more intelligent participants showed greater increases in functional connectivity of DMPFC and AG. These findings suggest a more dynamic adjustment of neural processing to varying cognitive demands in more intelligent individuals. Particularly when it comes to more difficult tasks, more intelligent people seem to be better able to down-regulate activity in the brain's default mode network. Due to the relatively small sample size, these findings must be considered preliminary. While their interpretation should therefore be treated with caution, they suggest conceptually new avenues for replication in larger samples. As far as the observed processes reflect the suppression of task-unrelated neural processing and a better focus on the task at hand, they can potentially explain the general performance advantage of more intelligent individuals across various cognitive tasks.