The semantic network at work and rest: Differential connectivity of anterior temporal lobe subregions

he anterior temporal lobe (ATL) makes a critical contribution to semantic cognition. However, the functional connectivity of the ATL and the functional network underlying semantic cognition has not been elucidated. Additionally, subregions of the ATL have distinct functional properties and thus the potential differential connectivity between these subregions requires investigation. We explored these aims utilising both resting-state and active semantic task data in humans in combination with a dual-echo gradient EPI paradigm designed to ensure signal throughout the anterior temporal lobe (ATL). In the resting state analysis, the ventral ATL and anterior middle temporal gyrus (MTG) were shown to connect to areas responsible for multimodal semantic cognition, including bilateral ATL, inferior frontal gyrus, medial prefrontal cortex, angular gyrus, posterior MTG and medial temporal lobes. In contrast, the anterior STG/STS was connected to a distinct set of auditory and language-related areas, including bilateral STG, pre- and postcentral gyri, supplementary motor area, supramarginal gyrus, posterior temporal cortex and inferior and middle frontal gyri. Complementary analyses of functional connectivity during an active semantic task were performed using a psychophysiological interaction (PPI) analysis. The PPI analysis highlighted the same semantic regions suggesting a core semantic network active during rest and task states. This supports the necessity for semantic cognition in internal processes occurring during rest. The PPI analysis showed additional connectivity of the ventral ATL to regions of occipital and frontal cortex. These areas strongly overlap with regions found to be sensitive to executively-demanding, controlled semantic processing.