The modular and integrative functional architecture of the human brain

Significance Many complex networks are composed of “modules” that form an interconnected network. We sought to elucidate the nature of the brain’s modular function by testing the autonomy of the brain’s modules and the potential mechanisms underlying their interactions. By studying the brain as a large-scale complex network and measuring activity across the network during 77 cognitive tasks, we demonstrate that, despite connectivity between modules, each module appears to execute a discrete cognitive function relatively autonomously from the other modules. Moreover, brain regions with diverse connectivity across the modules appear to play a role in enabling modules to interact while remaining mostly autonomous. This generates the counterintuitive idea that regions with diverse connectivity across modules are necessary for modular biological networks. Network-based analyses of brain imaging data consistently reveal distinct modules and connector nodes with diverse global connectivity across the modules. How discrete the functions of modules are, how dependent the computational load of each module is to the other modules’ processing, and what the precise role of connector nodes is for between-module communication remains underspecified. Here, we use a network model of the brain derived from resting-state functional MRI (rs-fMRI) data and investigate the modular functional architecture of the human brain by analyzing activity at different types of nodes in the network across 9,208 experiments of 77 cognitive tasks in the BrainMap database. Using an author–topic model of cognitive functions, we find a strong spatial correspondence between the cognitive functions and the network’s modules, suggesting that each module performs a discrete cognitive function. Crucially, activity at local nodes within the modules does not increase in tasks that require more cognitive functions, demonstrating the autonomy of modules’ functions. However, connector nodes do exhibit increased activity when more cognitive functions are engaged in a task. Moreover, connector nodes are located where brain activity is associated with many different cognitive functions. Connector nodes potentially play a role in between-module communication that maintains the modular function of the brain. Together, these findings provide a network account of the brain’s modular yet integrated implementation of cognitive functions.