Coexistence of the Social Semantic Effect and Non-Semantic Effect in the Default Mode Network

The default mode network (DMN) in the brain shows both semantic and non-semantic effects, sparking debate about its role in semantic processing. Four views exist: the DMN supports general semantics, semantic effects are confounded by task difficulty, the same DMN areas serve both semantic and non-semantic functions, or the DMN contains multiple subnetworks for different semantic aspects. An fMRI experiment found that within a DMN subnetwork called the social semantic network, all areas showed social semantic activation and difficulty-induced deactivation. The ventral angular gyrus, previously interpreted as showing only difficulty effects, exhibited social semantic activation independent of difficulty.

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Abstract

Abstract Neuroimaging studies have found both semantic and non-semantic effects in the default mode network (DMN), leading to an intense debate on the role of the DMN in semantic processes. Four different views have been proposed: 1) The general semantic view holds that the DMN contains several hub regions supporting general semantic processes; 2) the non-semantic view holds that the semantic effects observed in most regions of the DMN (especially the ventral angular gyrus) are confounded by difficulty and do not reflect semantic processing per se; 3) the multifunction view holds that the same areas in the DMN can support both semantic and non-semantic functions; and 4) the multisystem view holds that the DMN contains multiple subnetworks supporting different aspects of semantic processes separately. Using an fMRI experiment, we found that in one of the subnetworks of the DMN, called the social semantic network, all areas showed social semantic activation and difficulty-induced deactivation. The ventral angular gyrus, whose function had been interpreted according to the difficulty effect, showed social semantic activation independent of difficulty. In addition, the distributions of two non-semantic effects, that is, difficulty-induced and task-induced deactivations, showed dissociation in the DMN. Our findings provide two insights into the semantic and non-semantic functions of the DMN, which are consistent with both the multisystem and multifunction views: First, the same areas of the DMN can support both social semantic and non-semantic functions; second, similar to the multiple semantic effects of the DMN, the non-semantic effects also vary across its subsystems.