Neuropsychological Tractographic Assessment

Neurocognitive tractographic assessment (NTA) is an emerging field that aims at enhancing research and clinical practice based on the integration of neuropsychology, neuroimaging, bioinformatics, biophysics, and biomedicine. NTA combines different levels, including genetics, neurochemistry (hormones, neurotransmitters), cognitive microstructure (i.e. the study of neural networks by tractography), brain morphometry, cognitive ontologies (behavioral and mental concepts), and social scaffolding.

Diffusion-Weighted Magnetic Resonance Imaging (DW-MRI) is a technique that allows one to perform cerebral white matter (WM) tractography. In a simple way, whole-brain tractography shows the road network of information. The “highways” are formed by bundles, which connect some distant areas in order to generate cognitive processes. For example, the inferior fronto-occipital fasciculus is a large WM bundle running from executive-frontal cortex to visuo-occipital area. This fasciculus was found to be crucial for reading, semantic abstraction, and mood appraisal.

“ExploreDTI”, developed by Alexander Leemans, is a graphical toolbox for processing, analyzing, and visualizing the complex information derived from DW-MRI data acquisitions. One of its applications consists of obtaining group and individual statistics and descriptive measures about the brain’s connectivity degree. These measures, like fractional anisotropy and mean diffusivity, are considered to be biomarkers in neurological diseases.

The complex tractography data accounts for a complex system: the cerebromental object, which calls for a new ontology, or knowledge engineering. Cognitive microstructure interacts with the other levels of analysis, so this new ontology needs new metaphors. For example, the recipe metaphor, following Lisa Feldman Barret’s psychological primitives, states that ingredients of a cognitive-affective process are implemented in the behavior algorithm. Timing and loading of the cognitive capacities, implemented online, follow an algorithm observed in a space structured to obtain behavioral samples (e.g. a neuropsychological task), described with ‘agreed upon’ mental terms. NTA divides behavior (mental, actions) in minimal cognitive units. But there is nothing mind can do that brain cannot. Therefore, NTA is within the sciences of complexity, waiting for better fit models and technology developments that allow more direct brain imaging data, and genetic structures language.

In our work, “CogTract” (Cognition with Tracts), we use a specific tool in ExploreDTI to relate diffusion measures at each position along the fiber bundle trajectory with cognition and affection based indices (e.g., as obtained from behavioral and computerized tasks). The main goal is to develop a tractography based neuropsychological assessment that can improve cognitive treatment and rehabilitation. In this context, we will evaluate pre- and post-surgery structural brain conditions, investigating the trade-off between necessary tissue removal and preservation of information processing quality.