Patients with Mild Cognitive Impairment (MCI) or Subjective Cognitive Decline (SCD) may or may not develop Alzheimer's disease (AD) dementia. Yet identifying patients at risk is crucial: delaying the onset of the disease by 5 years could reduce prevalence by 50%. To achieve this, we need affordable biomarkers combined with clinically meaningful assessment tools. Current approaches (cognition, imaging or Tau and Amyloid peptide assays) lack precision or specificity (e.g., age-related memory deficits) and involve invasive and costly procedures, sometimes inaccessible in France (e.g., the "AT(N)" framework). Recently, quantitative diffusion MRI (dMRI) has identified in-vivo gray matter microstructural changes linked to hyperphosphorylated Tau protein, which are of great diagnostic value. Still, we ignore whether and how these changes are responsible for early memory impairment in AD. The MIMA-P project will combine multi-compartment models of the high-resolution diffusion signal with a cognitive assessment of memory based on recent models of medial temporal lobe function to assess the relevance of a new affordable, rapid and non-invasive early marker of the disease.
aged between 50 and 80
native French speaking
right-handed
with a level of education equal to or higher than the Certificat d'Etudes Primaires (primary school leaving certificate)
contraindications to MRI : Abdominal circumference + upper limbs stuck to the body > 200 cm; Implantable pacemaker or defibrillator; Neurosurgical clips; Cochlear implants ; Neural or peripheral stimulator; Intra-orbital or encephalic metallic foreign bodies; Endoprostheses fitted less than 4 weeks ago and osteosynthesis devices fitted less than 6 weeks ago; Claustrophobia.
sensory deficit interfering with experimental tests
pregnant or breast-feeding women
adults under legal protection (safeguard of justice, curatorship, guardianship), persons deprived of liberty
Parallel
high-resolution diffusion MRI
Diagnostic testThe study will combine multi-compartment models (e.g. Archer et al., 2020; Parker et al., 2020) of high-resolution diffusion MRI within medial temporal lobes regions of interest defined through the ASHS algorithm (Yushkevich et al., 2015), with theoretically driven cognitive assessment medial temporal lobes functions. The '4 mountains test' and the 'Memory entities' test will allow specific probing of hippocampal and rhinal cortices functions, respectively (Hartley et al., 2007; Besson et al., 2020).
Diffusion-MRI based parameters estimates of medial temporal lobe gray matter microstructure
Free-water and free-water corrected Fractional anisotropy are two parameters that can be estimated through Multi-Compartment Modelling of the diffusion MRI signal within medial temporal lobes gray matter. We will compute these parameters for the hippocampus and the surroundings rhinal cortices. These measures will be compared between patients and healthy controls.
Diffusion-MRI based parameters estimates of medial temporal lobe gray matter microstructure
Free-water and free-water corrected Fractional anisotropy are two parameters that can be estimated through Multi-Compartment Modelling of the diffusion MRI signal within medial temporal lobes gray matter. We will compute these parameters for the hippocampus and the surroundings rhinal cortices. These measures will be compared across patients groups.
Relationships between medial temporal lobe gray matter microstructure and memory
Free-water and free-water corrected Fractional anisotropy are two parameters that can be estimated through Multi-Compartment Modelling of the diffusion MRI signal within medial temporal lobes gray matter. We will compute these parameters for the hippocampus and the surroundings rhinal cortices. Memory accuracy scores will be computed for the two memory tasks "The '4 mountains test' and the 'Memory entities' test" . Correlational analyses will be performed across groups between gray matter microstructure estimates and memory scores.
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