Semantic Features and Concepts in the Left and Right Angular Gyrus
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Semantic features and concepts in the left and right angular gyrus Megan Reilly1, Natalya Machado1, David Badre1,2 and Sheila Blumstein1,2 1: Department of Cognitive, Linguistic and Psychological Sciences, Brown University 2: Brown Institute for Brain Science, Brown University Background fMRI Results • Patient research has investigated the role of the temporal lobe in processing semantic • Left hemisphere: significant main effect of category information • Right hemisphere: significant main effect of feature • Category-specific deficits (e.g. living things vs. nonliving things) distinctiveness • More vs. less specific information (e.g., ‘zebra – has stripes’ vs. ‘zebra – has four legs’) Left Angular Gyrus • No interactions or simple effects Right Angular Gyrus 0.05 • Angular gyrus (AG): involved in integration during semantic processing (Seghier, 2013) 0.05 • The left hemisphere is typically considered to be dominant but the right AG is implicated as well 0.00 0.00 Feature Feature • The left hemisphere may be important to verbal conceptual information while the right is −0.05 Distinctive −0.05 Distinctive * sensitive to low-level feature information (Gainotti, 2011) Shared Shared • Possible roles for the right angular gyrus: −0.10 −0.10 Percent signal change Percent • Plays a similar role in semantic processing to the left AG but less efficient at processing −0.15 signal change Percent −0.15 information at the level of the concept Living Nonliving Living Nonliving Category Category • Unique role in processing semantic features: crucial for normal semantic processing Behavioral lateralization: both hemispheres process shared features faster than distinctive features, but the right hemisphere is particularly slow to process distinctive features (Reilly, What role does the Angular Gyrus Machado & Blumstein, 2015) play in processing shared and TMS Results 1200 * distinctive semantic information? Left AG TMS Right AG TMS 1100 distinctive 150 150 shared Do the left and right Angular Gyri play RT (ms) RT • Left hemisphere: No effects 1000 100 100 sham) sham) − Feature − Feature different roles? 50 • Right hemisphere: simple 50 900 Distinctive effect for shared features of Distinctive left right 0 Shared 0 Shared living things * Hemisphere −50 −50 RT effect (real effect RT −100 (real effect RT −100 Living Nonliving Living Nonliving Category Category Methods • Stimuli: 384 living things (plants and animals) and nonliving artifacts (tools, weapons, household items, clothing, etc.) Conclusions • Each paired with one shared and one distinctive feature • The left AG is sensitive to semantic category but not necessarily to feature distinctiveness • Filler stimuli were paired with false features • TMS results do not provide evidence that the LAG plays a necessary role in semantic feature verification; may be influenced downstream by other areas in the semantic network • Participants: native English-speaking, right-handed adults who reported no history of neurological disorder • The right AG is sensitive to feature distinctiveness across categories • Consistent with the view that the left hemisphere processes verbal conceptual information while the right processes semantic information at the level of the • Functional magnetic resonance imaging (fMRI): N = 16 semantic feature • Transcranial magnetic stimulation (TMS) pilot: N = 6 • If the right hemisphere is sensitive only to feature-level effects, the feature verification task may elicit right AG activation while other tasks in the literature (e.g., • Imaging: 3T Trio scanner with 32-channel head coil; TR = 2500 picture naming) do not ms • The right AG appears to play a crucial role in processing the shared features of living things • ROI analysis on anatomically-defined AG in each hemisphere • These are also the features which are more preserved in temporal lobe patients (Moss et al., 1998) using Talairach atlas in AFNI Shared Distinctive • Suggests a separate role for semantic processing in the right AG outside of the core frontotemporal network • TMS: MagStim Rapid Plus boots boots Nonliving worn in winter worn by cowboys • Offline continuous theta-burst stimulation and sham zebra zebra stimulation: 600 pulses delivered in 50-Hz 3-pulse triplets at has four legs has stripes 200-ms intervals Living • Sites: left AG and right AG, real and sham stimulation to each References and Acknowledgments site (+/- 47, -69, 43) Gainotti (2011). The organization and dissolution of semantic-conceptual knowledge: Is the “amodal hub” the only plausible model? Brain and Cognition 75(3), 299-309. • Stimulation at 80% of active motor threshold Moss et al. (1998). ‘Two eyes of a see-through’: Impaired and intact semantic knowledge in a case of selective deficit for living things. Neurocase 4(4-5), 291-310. Reilly, Machado & Blumstein (2015). Hemispheric lateralization of semantic feature distinctiveness. Neuropsychologia 75, 99-108. • Task: participants verified features using a button press (yes/ Seghier (2013). The angular gyrus: Multiple functions and multiple subdivisions. The Neuroscientist 19(1), 43-61. no) This research funded by: American Association of University Women Dissertation Fellowship, NIH grant R01 DC006220, Brown Institute for Brain Science .