The spatiotemporal dynamics of semantic integration in the human brain

Abstract

AbstractLanguage depends critically on the integration of lexical information to derive semantic concepts. The neurobiology of this fundamental aspect of human cognition remains mostly unknown. Limitations of spatiotemporal resolution have previously rendered it difficult to disentangle processes involved in semantic integration from independent computations such as tracking word meaning and establishing referents. We utilized intracranial recordings (n = 58) during the presentation of orthographic descriptions that were either referential or non-referential to a common object. Referential contexts enabled high frequency broadband gamma activation (70–150 Hz) of a distributed network including the inferior frontal sulcus (IFS), medial parietal cortex (MPC) and medial temporal lobe (MTL) in the left, language-dominant hemisphere. Components of this network (IFS, MPC), alongside posterior superior temporal sulcus, showed greater engagement for trials that did not progressively isolate a limited set of referents, relative to trials that did. IFS and posterior middle temporal gyrus activity was modulated by semantic coherence, regardless of whether the sentence picked out a common object. Centered around IFS and spreading out dorsally towards middle frontal gyrus and ventrally towards anterior/posterior inferior frontal gyrus, we uncovered a cortical mosaic of functional specialization for reference, coherence and semantic narrowing. Early processing windows implicated IFS in all aspects of semantics, and in later windows sub-portions of IFS exposed a clearer functional tessellation with some remaining overlap. This work unveils how lateral fronto-temporal regions make distinctly rich semantic contributions and are involved jointly in semantic integration and conflict resolution, depending on the sub-region and processing stage.