Matthew Lambon Ralph vs Jeffrey R. Binder
Role of Angular Gyrus in Semantic Processing

Saturday, October 27 from 5:50 – 7:20 pm, Kursaal Auditorium

 

Matt Lambon Ralph is Professor of Cognitive Neuroscience and Associate Vice-President (Research) at the University of Manchester (UK). He and his colleagues within the Neuroscience and Aphasia Research Unit (NARU) explore the neural basis of semantic cognition, language and their disorders utilizing multiple clinical and cognitive neuroscience techniques. They also use the same approach to explore and understand study of the neural and cognitive principles that guide recovery and rehabilitation.

Abstract:
The role of the angular gyrus (AG) in semantic cognition (semantically-driven expressive and receptive behaviour) is firmly established from a long history of neuropsychological and, more latterly, functional neuroimaging studies. Its exact contribution to semantic processing is unclear, however. Two alternative accounts are found in the classic and contemporary neuroscience literatures.  One view is that the transmodal AG’s contribution is primarily representational. The alternative account is that the AG forms part of a distributed neural network that supports ‘semantic control’ – that is, the ability to manipulate underlying semantic knowledge within the current context in order to generate time- and task-appropriate behaviour (both verbal and nonverbal).  Both classic and contemporary neuropsychological studies have found that, like patients with ventral prefrontal damage, lesions to posterior temporoparietal regions does not lead to a representational deficit but rather to poor semantic control (in both verbal and nonverbal tasks). Convergent evidence for this hypothesis has been found in contemporary functional neuroimaging and TMS studies – which also provide greater neuroanatomical specificity than that offered by neuropsychological investigations alone. This hypothesis about AG functioning offers the potential of a unified account, not only for semantic cognition, but also the role of the AG in episodic memory, cognitive control and syntactic processing.

Jeffrey R. Binder is Professor of Neurology and Biophysics and Director of the Language Imaging Laboratory at the Medical College of Wisconsin, Milwaukee, USA. He and his colleagues investigate the neurobiological basis of language using multimodal imaging and behavioral techniques, with particular emphasis on basic speech perception, reading, and semantic processes. Binder and colleagues also work on development and validation of fMRI and MEG methods for preoperative language mapping in epilepsy.

Abstract:
An extensive body of evidence from functional imaging studies links the angular gyrus (AG) with semantic processing. This evidence shows stronger responses in both left and right AG with increasing information content, indicating a specific role in semantic representation. Other regions, including neighboring cortex in the intraparietal sulcus and posterior temporal lobe, show the opposite pattern, with stronger responses to semantically impoverished stimuli, which engage additional controlled search and attention mechanisms. Damage to the AG impairs sentence comprehension and retrieval of thematic relations, suggesting a role in representing associative and temporospatial knowledge. This role is consistent with the anatomical location of the AG at the convergence of high-level spatial, visual motion, and kinesthetic representational systems. Variation in performance with varying task procedures in patients with semantic aphasia has been interpreted as indicating a deficit of semantic control, but can be explained by accompanying damage to attentional and phonological systems. The relative lack of item consistency in tests of object knowledge in these patients is expected given that their core deficit does not involve object concepts, but rather relational and event concepts.