The Royal Road to Semantic Cognition: Untangling Semantic Components in Temporal Lobe

Abstract

Functional magnetic resonance imaging (fMRI) research into semantic cognition has returned highly variable results, especially in anterior temporal regions. One likely reason for this variability is that tasks used to investigate this topic are believed to engage only shallow semantic processing. Another reason is that certain classes of stimuli (particularly abstract words) are often confounded by un-modeled social or emotional content; many researchers believe that it is this social and emotional information, rather than general semantic information per se, that elicits response in ATL. Our experiments use a task designed to elicit deep semantic processing (the triads task) along with explicit investigation into the social and emotional content of semantic stimuli to try to pry these factors apart and characterize the temporal lobes in general, and the ATLs in particular, with regard to their involvement in semantic cognition. We find that, contrary to some reports, the ATL is highly involved in semantic processing even in its most anterior aspects; that counter to prominent theories this involvement is not (or is not always) due to the inclusion of social or emotional content in the stimuli; and that a semantic task that engages deep semantic processing has an activation signature that closely resembles the signature of full-sentence processing, despite the seeming un-structured nature of the processing required by the triads task. We propose a general role for ATL as semantic integrator to characterize these disparate findings.