Network Controllability in the IFG Relates to Controlled Language Variability and Susceptibility to TMS

TL;DR

This study models the left inferior frontal gyrus as a network control point in the brain, linking its controllability to language task performance and susceptibility to TMS, revealing how brain network dynamics influence language processing.

Contribution

It introduces a novel network control framework to understand the role of the LIFG in language production and TMS effects, integrating brain connectivity with cognitive control.

Findings

LIFG controllability predicts TMS vulnerability in language tasks.

Network control metrics explain TMS-induced performance changes.

Controllability of communication across brain modules relates to language task effects.

Abstract

In language production, humans are confronted with considerable word selection demands. Often, we must select a word from among similar, acceptable, and competing alternative words in order to construct a sentence that conveys an intended meaning. In recent years, the left inferior frontal gyrus (LIFG) has been identified as critical to this ability. Despite a recent emphasis on network approaches to understanding language, how the LIFG interacts with the brain's complex networks to facilitate controlled language performance remains unknown. Here, we take a novel approach to understand word selection as a network control process in the brain. Using an anatomical brain network derived from high-resolution diffusion spectrum imaging (DSI), we computed network controllability underlying the site of transcranial magnetic stimulation in the LIFG between administrations of two word selection tasks. We find that a statistic that quantifies the LIFG's theoretically predicted control of difficult-to-reach states explains vulnerability to TMS in language tasks that vary in response (cognitive control) demands: open-response (word generation) vs. closed-response (number naming) tasks. Moreover, we find that a statistic that quantifies the LIFG's theoretically predicted control of communication across modules in the human connectome explains TMS-induced changes in open-response language task performance only. These findings establish a link between network controllability, cognitive function, and TMS effects.