Traumatic Brain Lesion Quantification based on Mean Diffusivity Changes

International audienceWe report the evaluation of an automated method for quantification of brain tissue damage, caused by a severe traumatic brain injury, using mean diffusivity computed from MR diffusion images. Our automatic results obtained on realistic phantoms and real patient images 10 days post-event provided by nine different centers were coherent with four expert manually identified lesions. For realistic phantoms automated method scores were equal to 0.77, 0.77 and 0.83 for Dice, Precision and Sensibility respectively compared to 0.78, 0.72 and 0.86 for the experts. The inter correlation class (ICC) was 0.79. For 7/9 real cases 0.57, 0.50 and 0.70 were respectively obtained for automated method compared to 0.60, 0.52 and 0.78 for experts with ICC=0.71. Additionally, we detail the quality control module used to pool data from various image provider centers. This study clearly demonstrates the validity of the proposed automated method to eventually compute in a multi-centre project, the lesional load following brain trauma based on MD changes

Individual differences in neural architecture supporting mental time travel

Episodic and semantic memory have been cornerstones of memory research ever since they were first described in a seminal article by Endel Tulving in 1972. Later work by Tulving posited that particularly episodic memory supported mental time travel, a process by which humans could project the self across a conceptual lifespan (however modern research has emphasised the role of semantic memory in the process). Various neurocognitive models have been proposed that attempt to explain the component processes of mental time travel. While it is now recognized that a common ‘core’ brain network underlies memory, prospection, and imagination (Schacter et al., 2017), the neural substrates of the component processes that comprise the core network supporting memory-based simulations, and the extent to which they are dissociable, are still a matter of intense debate. This thesis has demonstrated that combining diffusion MRI-based tractography with interview and self-report measures is a viable method for investigating the associations between interindividual differences in white matter microstructure and cognitive traits or tendencies related to mental time travel. The present findings provide support for the notion that episodic and semantic memory systems are at least partially separate and supported by different structurally instantiated neural pathways. However, it is also clear that they must interact and support each other within episodic construction and mental time travel. Regarding the current models of mental time travel, the results of this thesis do not provide overwhelming support to any single model. However, some evidence has been provided (linking fornix-mediated hippocampal processing to spatial components of memory in particular) that might support the scene construction hypothesis (Hassabis & Maguire, 2007). Further, present findings did not show a significant association between semantic circuitry (mediated by the ILF) and episodic future thinking – which poses a challenge to the semantic scaffolding hypothesis (Irish & Piguet, 2013). However, this is consistent with Tulving’s original notion of episodic and semantic memory (including autobiographical facts) being dissociable but interacting memory systems that are future as well as past directed