How the Brain Creates Unity and Diversity of Executive Functions

Excerpt

Different executive functions, such as response inhibition, working memory updating, and mental set shifting, are correlated but separable. The focus of this chapter is the neural substrates of this “unity and diversity,” with particular reference to the “multiple demand” (MD) system, a set of well-localized frontal, parietal, and posterior temporal brain regions that are active in tasks with diverse cognitive demands. After evidence for unity and diversity in behavioral studies is reviewed, the anatomy and function of the MD system is described and its potential mapping to unity and diversity discussed. Unity is evident in strong patterns of activation in core MD regions across tasks with different demands. Diversity is evident in differential activation of adjacent, more domain-specific regions, with strongest activation sometimes at the boundary between the MD core and these adjacent regions, suggesting communication between the two. It is suggested that the MD core serves to combine information from many brain regions and networks, integrating the diverse contents of an attended cognitive operation. Overlaps of the MD system and executive function unity with general cognitive ability are discussed, as are difficulties in integrating studies focusing on group-mean contrasts with individual-differences results. Understanding how behavior arises from the brain will involve understanding how information is represented, communicated, and transformed within and between brain networks, with the MD system likely contributing a core, integrative role.