Depending on the point of view, different definitions of aging have been proposed. Thus, at the biological level, aging corresponds to a natural physiological process that leads to the progressive degeneration of cells and the slowing down of the vital functions of a living organism. More generally, aging is a multifactorial and multidimensional process that occurs at the cognitive, social, biological or psychological level.

The primary objective of this study is to evaluate the balance between activation (Task-Positive Network : TPN-Language, L, TPN-Verticality, V) and rest (Task-Negative Network : TNN) activity during normal aging, in two domains (language and posturo-spatial perception of verticality).

From a cognitive point of view, although healthy older people become slower to analyze information, they remain just as accurate as young adults in performing different cognitive tasks. This necessarily implies compensation processes, with new cognitive strategies and a restructuring of the brain networks underlying these processes. These compensatory phenomena are known under the general name of neurocognitive reserve.

Specific functions such as language, visuospatial skills, motor control, posture, or memory, are affected in a very variable way among the elderly. This variability involves multiple cognitive profiles rather than just one form of aging. Indeed, healthy aging can be defined cognitively in two ways, as a homogeneous or rather heterogeneous process. According to the homogeneous hypothesis of aging, the behavioral, cognitive and brain-like manifestations are similar among the elderly, without differentiation between functions. In other words, according to this hypothesis, aging would affect all the elderly and cognitive processes in the same way. Conversely, according to the heterogeneous hypothesis, significant differences should be revealed between individuals and in the same individual according to different cognitive processes. This heterogeneity is explained by multiple factors (genetic, environmental, societal, educational, or lifestyle). If neuropsychological tests or behavioral experiments (and performance of the task) allow to identify rather easily the differences encountered among the elderly in terms of cognitive heterogeneity, this differential activity at the cerebral level is more difficult to highlight. Functional neuroimaging methods and techniques can provide a pathway for this purpose, to provide both spatial information (involved brain regions) and temporal information (dynamics of brain activation) when performing cognitive tasks or when the rest period.

In this context, the magnetoencephalography (MEG) method is a preferred technique that can provide all these types of information on brain activity. Two types of networks can therefore be recorded : task-positive network (TPN) activated when the participant is involved in a task (in this project, language and posture / verticality), and task-negative network (TNN) specific to the state of rest , represented by regions that are called "deactivated". These two networks will therefore be characterized in the study by the following parameters: (a) network: set of regions involved; (b) temporal dynamics of their activity, and (c) functional connectivity between the regions of TPN and TNN.

To answer the question of homogeneity vs. heterogeneity of cognitive cerebral aging, TPNs vs. TNN will be compared in a group of healthy young adults compared to a group of healthy elderly subjects. The comparison will be made for the three categories of parameters mentioned above (a-c).

Inclusion Criteria:

• Healthy volunteers from 25 to 85 years old : young group (25-49 years) / aged group (50 to 85 years)
• Right-handed
• Signed informed consent
• French mother tongue
• Speaking fluent French
• Normal or corrected view
• Medical examination conducted prior to participation in the trial
• Registered in the French social security scheme

Exclusion Criteria:

• Contraindication to Magnetoencephalography (MEG) and/or Magnetic resonance imaging (MRI) : implanted material, claustrophobia,…
• Generally severe condition: cardiac, respiratory, hematological, kidney, liver, cancer
• Regular use of anxiolytics, sedatives, antidepressants, neuroleptics
• Psychiatric pathology characterized
• Alcohol ingestion before the exam
• All categories of protected persons (Pregnant or lactating women, persons subject to a legal protection measure, persons deprived of their liberty by judicial or administrative decision)
• Alcohol ingestion before the exam
• Participation in other ongoing clinical trial with exclusion period or in the previous week
• Score MINI MENTAL STATE EXAMINATION (MMSE) < 24