Abstract
Awake humans constantly extract conceptual information from a flow of perceptual inputs. Category membership (e.g., is it an animate or inanimate thing?) is a critical semantic feature used to determine the appropriate response to a stimulus. Semantic representations are thought to be processed along a posterior-to-anterior gradient reflecting a shift from perceptual (e.g., it has eight legs) to conceptual (e.g., venomous spiders are rare) information. One critical region is the anterior temporal lobe (ATL): patients with semantic variant primary progressive aphasia (svPPA), a clinical syndrome associated with ATL neurodegeneration, manifest a deep loss of semantic knowledge.
Here, we test the hypothesis that svPPA patients, in the absence of an intact ATL, perform semantic tasks by over-recruiting areas implicated in perceptual processing. We acquired MEG recordings of 18 svPPA patients and 18 healthy controls during a semantic categorization task. While behavioral performance did not differ, svPPA patients showed greater activation over bilateral occipital cortices and superior temporal gyrus, and inconsistent engagement of frontal regions.
These findings indicate a pervasive reorganization of brain networks in response to ATL neurodegeneration: the loss of this critical hub leads to a dysregulated (semantic) control system, and defective semantic representations are compensated via enhanced perceptual processing.
Competing Interest Statement
The authors have declared no competing interest.
