title: Separate neural systems support representations for actions and objects during narrative speech in post-stroke aphasia.
abstract: BACKGROUND
  Representations of objects and actions in everyday speech are usually materialized as nouns and verbs, two grammatical classes that constitute the core elements of language. Given their very distinct roles in singling out objects (nouns) or referring to transformative actions (verbs), they likely rely on distinct brain circuits.
  
  
  METHODS
  We tested this hypothesis by conducting network-based lesion-symptom mapping in 38 patients with chronic stroke to the left hemisphere. We reconstructed the individual brain connectomes from probabilistic tractography applied to magnetic resonance imaging and obtained measures of production of words referring to objects and actions from narrative discourse elicited by picture naming tasks.
  
  
  RESULTS
  Words for actions were associated with a frontal network strongly engaging structures involved in motor control and programming. Words for objects, instead, were related to a posterior network spreading across the occipital, posterior inferior temporal, and parietal regions, likely related with visual processing and imagery, object recognition, and spatial attention/scanning. Thus, each of these networks engaged brain areas typically involved in cognitive and sensorimotor experiences equivalent to the function served by each grammatical class (e.g. motor areas for verbs, perception areas for nouns).
  
  
  CONCLUSIONS
  The finding that the two major grammatical classes in human speech rely on two dissociable networks has both important theoretical implications for the neurobiology of language and clinical implications for the assessment and potential rehabilitation and treatment of patients with chronic aphasia due to stroke.
authors.affiliation: Department of Neurology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: Ezequiel
authors.initials: E
authors.lastname: Gleichgerrcht
authors.affiliation: Department of Communication Sciences and Disorders, University of South Carolina, Columbia, SC, USA.
authors.forename: Julius
authors.initials: J
authors.lastname: Fridriksson
authors.affiliation: Department of Psychology, University of South Carolina, Columbia, SC, USA.
authors.forename: Chris
authors.initials: C
authors.lastname: Rorden
authors.affiliation: Department of Neurology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: Travis
authors.initials: T
authors.lastname: Nesland
authors.affiliation: Department of Psychology, University of South Carolina, Columbia, SC, USA.
authors.forename: Rutvik
authors.initials: R
authors.lastname: Desai
authors.affiliation: Department of Neurology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Bonilha
mesh_terms: D001037:Aphasia / Q000209:etiology / Q000473:pathology*; D001921:Brain / Q000473:pathology*; D063132:Connectome; D007839:Functional Laterality; D006801:Humans; D007807:Language Tests; D008279:Magnetic Resonance Imaging; D013060:Speech; D013068:Speech Production Measurement; D020521:Stroke / Q000150:complications*
keywords: Connectome; Diffusion tensor imaging; Discourse; Magnetic resonance imaging; Network-symptom mapping; Nouns; Stroke; Verbs