New brain scan method aims to spot Alzheimer's and Parkinson's early

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * For all participants: * French mother tongue * right-handed * with a level of education equal to or higher than the Certificat d'Études Primaires (Primary School Certificate) * Free of any medical or psychiatric condition likely to interfere with cognition (excluding diagnosis for patients) * Affiliated with a social security scheme * Having received oral and written information about the protocol and having signed a consent form to participate in this research. DCS+ group: \- Meeting the diagnostic criteria for "subjective cognitive decline-plus" (Jessen criteria (Jessen et al., 2014). Alzheimer's patients "Mild Cognitive Impairment due to Alzheimer's Disease," "MCI-MA": \- Meeting the diagnostic criteria for "Mild neurocognitive disorder due to Alzheimer's disease" (criteria of (Albert et al., 2011)) De novo" Parkinsonian patients, "MPdn": \- Presenting with newly diagnosed ("de novo") Parkinson's disease and free of cognitive deficits (criteria of Postuma et al., 2015 (Postuma et al., 2015)) Parkinsonian patients with "Mild Cognitive Impairment, "MCI-MP": \- Presenting Parkinson's disease associated with "mild neurocognitive impairment" (criteria of Litvan et al., 2012 (Litvan et al., 2012)) Exclusion Criteria: * All participants (healthy volunteers and patients) * Contraindications to MRI : * Abdominal circumference + upper limbs sticking 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. * Pregnant or breast-feeding women; * Adults under legal protection (safeguard of justice, curatorship, guardianship), persons deprived of liberty. Patients only * Score \>2 on the modified Hachinski scale (Hachinski et al., 2012) * Dementia according to McKhann criteria (McKhann et al., 2011) * Sensory deficit interfering with experimental tests Healthy volunteers only \- Cognitive impairment (MoCA score \< 26)