Inner speech (the "little voice" in our heads) plays a central role in our ability to perform complex cognitive tasks such as problem solving, reading, writing, thinking, and self awareness. It is estimated that at least a quarter of our lives is accompanied by inner speech, whether deliberate (mentally making a list) or more spontaneous (mind wandering). Although central to human life, its neural bases remain poorly understood. It has been recently discovered a single region in the human prefrontal cortex absent in nonhuman primates, the prefrontal operculum (PFO), which shows a pattern of functional connectivity with the rest of the brain that could give it a role in controlling inner speech. The aim of this research is to understand how the brain generates and controls inner speech using functional magnetic resonance imaging (fMRI). Dysfunctions of inner speech, especially when spontaneous and wandering, can lead to severe mental disorders (anxiety disorders, depression, verbal auditory hallucinations). It is therefore crucial to identify the role of the PFO and the networks that involve it, particularly the precuneus, in controlling inner speech across its different manifestations. The first hypothesis is that the PFO and the networks that include it play a key role in the cognitive control of inner speech in participants who experience inner speech. The second hypothesis is that the PFO is hyperactive in participants who lack inner speech (so called aphantasics), preventing the production of inner speech. To test these hypotheses, participants will complete a battery of well established questionnaires to determine whether they can produce inner speech (control participants with typical inner speech) or not (aphantasic participants). These participants will take part in an fMRI study contrasting tasks that recruit inner speech that do or do not require cognitive control. The third hypothesis is that the extent of inner speech depends on the capacity for self representation, and thus on the interaction between the PFO and the precuneus. The investigator hypothesize a positive correlation between inner speech ability and self representation capacity, associated with stronger functional connectivity between the PFO and the precuneus. The investigator predict reduced self representation in aphantasic participants. To test this, participants will complete a battery of well established questionnaires. The investigator will compute correlations between 1) behavioral performance on inner speech tasks and questionnaire scores, and 2) the network measures identified in fMRI (task activation and connectivity) and questionnaire scores.

Inclusion Criteria:

• Registered with the national Social Security system.
• Right handed.
• Native French speakers.
• Visual acuity sufficient to read stimuli (contact lenses permitted).
• Willing to follow MRI instructions and recommendations.
• Able to provide written informed consent to participate in the study.

Exclusion Criteria:

• History of known neurological or psychiatric disorder.

  • Respiratory pathologies (in particular persistent asthma) or cardiovascular diseases.

  • Speech or language disorders (aphasia, dysphasia, dysarthria, stuttering, etc.).

  • Hearing impairments.

  • Memory disorders.

  • Cognitive impairments limiting understanding of instructions.

  • Recent use of psychotropic medications. Major treatments not permitted in this research include psychotropic drugs that can alter perception, sensations, mood, consciousness, or behavior, for example:

    • Antipsychotics (valproic acid, amisulpride, aripiprazole, clozapine, cyamemazine, haloperidol, loxapine, olanzapine, risperidone).
    • Antidepressants (amitriptyline, citalopram, clomipramine, duloxetine, escitalopram, fluoxetine, mianserin, mirtazapine, nortriptyline, paroxetine, sertraline, venlafaxine).
    • Anxiolytics.

  • Pregnant or breastfeeding women. No pregnancy test will be performed at inclusion; pregnancy must be reported by self declaration.

  • Minors.

  • Persons deprived of liberty by judicial or administrative decision.

  • Persons admitted to a health or social institution for reasons other than research.

  • Adults under legal protection measures (guardianship, conservatorship).

  • Persons not affiliated with a social security scheme or with a similar scheme only.

  • Participants refusing to be informed in case of an incidental finding on MRI.

  • Contraindications to fMRI, including:

    • Pacemaker, neurosensory stimulator, or implantable defibrillator: risk of transient or permanent device damage or heating of metal parts. In patients with such devices, scanning should be performed only if absolutely necessary, with the patient's informed agreement after clear explanation of risks, and in the presence of a physician from the referring service.
    • Metallic prostheses: potential for significant artifacts depending on size and ferromagnetic properties; certain neurosurgical clips or cardiac valves may pose problems and require verification of the exact implanted model.
    • Ferromagnetic ocular or intracranial foreign bodies near nervous structures: risk of displacement and ocular or cerebral injury.
    • Cochlear implants: risk of demagnetization, electrode heating, and artifacts.
    • Neurosurgical shunt valves.
    • Claustrophobic participants.
    • Dental appliances.