Uncovering the Cognitive and Neural Mechanisms Underlying Cognitive Time

Inclusion Criteria: 1. Membership of a social security scheme or beneficiary of such a scheme. 2. At least 7 years' schooling. 3. Acceptance and signature of the informed consent form 4. Fluency in French (as assessed by the project leader) 5. Age between 20 and 35 years inclusive for young healthy subjects, and between 60 and 85 years inclusive for elderly healthy subjects. 6. Effective contraception for women of childbearing age: Contraception will be considered effective from the moment the participant declares taking an oral contraceptive, the presence of an IUD, diaphragm or contraceptive implant, or the performance of a tubal ligation or sterilisation. 7. Absence of global cognitive deficit attested by a score on the MOCA scale greater than or equal to 26/30. Exclusion Criteria: 1. Persons under guardianship, curators or safeguard of justice. 2. Pregnant women, women in labor and nursing mothers 3. Chronic neurological conditions 4. Uncorrected visual difficulties 5. Encephalitis 6. Endocrine or liver disease 7. History of head trauma with loss of consciousness lasting more than one hour 8. History of cancer in the last 5 years, with the exception of squamous cell carcinoma of the skin 9. Presence or history of chronic alcoholism or drug addiction 10. Presence of clinically significant major psychiatric disorders (according to DSM-IV-TR criteria) or symptoms that could affect the participant's ability to complete the research. 11. Use of medications that may modulate the dopaminergic system (psychotropic, with the exception of sleeping pills or occasional use of anxiolytics, as decided by the principal investigator). 12. Contraindications to MRI examination (pregnancy; pacemaker or neurosensory stimulator or implantable defibrillator; clip on an aneurysm or clip on a vascular malformation of the brain; intraocular or cerebral ferromagnetic foreign body; prosthesis or mobilizable ferromagnetic metal object or splinter; cochlear implant ; peripheral stimulator; neurosurgical ventriculoperitoneal shunt valves; permanent eyelid or lip make-up; jewelry or piercing that cannot be removed; certain tattoos depending on the type of ink, size and location; automated injection devices such as insulin pumps, blood glucose sensors, claustrophobia). 13. Radiotracer contraindications: Hypersensitivity to product excipients, chronic alcoholism, kidney disease. 14. Participation in research involving exposure to ionizing radiation (nuclear medicine or radiology examinations) in the year preceding inclusion or during a period of exclusion from other research.