The White Matter Module-Hub Network of Semantics Revealed by Semantic Dementia

International audience2AbstractCognitive neuroscience exploring the architecture of semantics has shown that coherent supra-modal concepts are computed in the anterior temporal lobes (ATL) but it is unknown how/where modularinformation implemented by posterior cortices (word/object/face forms) is conveyed to the ATL hub. We investigated the semantic module-hub network in healthy adults (N = 19) and in semantic dementia patients (N = 28) by combining semantic assessments of verbal and non-verbal stimuli and MRI-based fiber tracking usingseeds in three module-related cortices implementing i) written word forms (‘Visual Word Form Area’), ii) abstract lexical representations (posterior-superior temporal cortices), and iii) face/object representations (‘Face Form Area’).Fiber tracking revealed three key tracts linking the ATL with the three module-related cortices. Correlation analyses between tract parameters and semantic scores indicated that the three tracts subserve semantics, transferring modular verbal or non-verbal object/face information to the left and right ATL, respectively. The module-hub tracts were functionally and micro-structurally damaged in semantic dementia whereas damage to non-module specific ATL tracts (inferior longitudinal fasciculus, uncinate fasciculus) had more limited impact on semantic failure. These findings identify major components of the white matter module-hub network of semantics and they corroborate/materialize claims of cognitive models positing direct links between modular and semantic representations. In combination with modular accounts of cognition, they also suggest that the currently prevailing ‘hub-and-spokes’ model of semantics could be extended by incorporating an intermediate module level containing invariant representations, in addition to ‘spokes’ which subserve the processing of a near-unlimited number of sensori-motor and speech-sound features