Neural Activity in the Fronto-Parietal Multiple Demand Network Robustly Predicts Individual Differences In Working Memory And Fluid Intelligence

A bilateral network of frontal and parietal domain-general brain regions - the multiple demand (MD) system (Duncan, 2010, 2013) - has been linked to our ability to engage in goal-directed behaviors, solve novel problems, and acquire new skills. Damage to this network leads to deficits in executive abilities and lower fluid intelligence (e.g., Woolgar et al., 2010), and aberrant functioning of this network has been reported in a variety of neurological and psychiatric disorders (e.g., Cole et al., 2014). However, prior attempts to link MD activity to behavior in neurotypical adults have yielded contradictory findings. In a large-scale fMRI study (n=140), we found that stronger up-regulation of the MD activity with increases in task difficulty, as indexed by larger differences between responses to the harder vs. easier condition, was associated with better behavioral performance on the working memory task performed in the scanner, and overall higher fluid intelligence measured independently. We further demonstrate how small samples, like those used in some earlier studies, could have led to the opposite patterns of results. Finally, the relationship we observed between MD activity and behavior was selective: neural activity in another large-scale network (the fronto-temporal language network) did not reliably predict working memory performance or fluid intelligence. Our study thus paves the way for using individual fMRI measures to link genetic and behavioral variation in executive functions in healthy and patient populations.