title: Automatic and Controlled Semantic Retrieval: TMS Reveals Distinct Contributions of Posterior Middle Temporal Gyrus and Angular Gyrus.
abstract: Semantic retrieval involves both (1) automatic spreading activation between highly related concepts and (2) executive control processes that tailor this activation to suit the current context or goals. Two structures in left temporoparietal cortex, angular gyrus (AG) and posterior middle temporal gyrus (pMTG), are thought to be crucial to semantic retrieval and are often recruited together during semantic tasks; however, they show strikingly different patterns of functional connectivity at rest (coupling with the "default mode network" and "frontoparietal control system," respectively). Here, transcranial magnetic stimulation (TMS) was used to establish a causal yet dissociable role for these sites in semantic cognition in human volunteers. TMS to AG disrupted thematic judgments particularly when the link between probe and target was strong (e.g., a picture of an Alsatian with a bone), and impaired the identification of objects at a specific but not a superordinate level (for the verbal label "Alsatian" not "animal"). In contrast, TMS to pMTG disrupted thematic judgments for weak but not strong associations (e.g., a picture of an Alsatian with razor wire), and impaired identity matching for both superordinate and specific-level labels. Thus, stimulation to AG interfered with the automatic retrieval of specific concepts from the semantic store while stimulation of pMTG impaired semantic cognition when there was a requirement to flexibly shape conceptual activation in line with the task requirements. These results demonstrate that AG and pMTG make a dissociable contribution to automatic and controlled aspects of semantic retrieval.
  
  
  CONCLUSIONS
  We demonstrate a novel functional dissociation between the angular gyrus (AG) and posterior middle temporal gyrus (pMTG) in conceptual processing. These sites are often coactivated during neuroimaging studies using semantic tasks, but their individual contributions are unclear. Using transcranial magnetic stimulation and tasks designed to assess different aspects of semantics (item identity and thematic matching), we tested two alternative theoretical accounts. Neither site showed the pattern expected for a "thematic hub" (i.e., a site storing associations between concepts) since stimulation disrupted both tasks. Instead, the data indicated that pMTG contributes to the controlled retrieval of conceptual knowledge, while AG is critical for the efficient automatic retrieval of specific semantic information.
authors.affiliation: Deparment of Psychology and York Neuroimaging Centre, University of York, York YO10 5DD, United Kingdom, and.
authors.forename: James
authors.initials: J
authors.lastname: Davey
authors.affiliation: Department of Psychology, Northumbria University, Tyne and Wear NE1 8ST, United Kingdom.
authors.forename: Piers L
authors.initials: PL
authors.lastname: Cornelissen
authors.affiliation: Deparment of Psychology and York Neuroimaging Centre, University of York, York YO10 5DD, United Kingdom, and.
authors.forename: Hannah E
authors.initials: HE
authors.lastname: Thompson
authors.affiliation: Deparment of Psychology and York Neuroimaging Centre, University of York, York YO10 5DD, United Kingdom, and.
authors.forename: Saurabh
authors.identifier: http://orcid.org/0000-0002-4439-0579
authors.initials: S
authors.lastname: Sonkusare
authors.affiliation: Deparment of Psychology and York Neuroimaging Centre, University of York, York YO10 5DD, United Kingdom, and.
authors.forename: Glyn
authors.initials: G
authors.lastname: Hallam
authors.affiliation: Deparment of Psychology and York Neuroimaging Centre, University of York, York YO10 5DD, United Kingdom, and.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Smallwood
authors.affiliation: Deparment of Psychology and York Neuroimaging Centre, University of York, York YO10 5DD, United Kingdom, and beth.jefferies@york.ac.uk.
authors.forename: Elizabeth
authors.identifier: http://orcid.org/0000-0002-3826-4330
authors.initials: E
authors.lastname: Jefferies
mesh_terms: D001245:Association Learning / Q000502:physiology; D001931:Brain Mapping; D003210:Concept Formation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007600:Judgment / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D010296:Parietal Lobe / Q000502:physiology*; D010775:Photic Stimulation; D012660:Semantics; D013702:Temporal Lobe / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: angular gyrus; control; posterior middle temporal gyrus; semantic; transcranial magnetic stimulation