Inclusion Criteria:  Male ou female volunteers, who are between 18 and 50 years old, With a BMI (Body Mass Index) between 18.5 and 25 kg/m2, Not having subjective EDS (Excessive Daytime Sleepiness) : total score at ESS (Epworth Sleepiness Scale) lower or equal to 11, Not having insomnia complaints (ISI total score lower than 8), Having a SCL90R (Symptom Check List- 90 items Revised) score lower than 60 (only for Anxiety and Depression categories' items of the checklist), Regular bedtime between 22H00 and 0H00, regular get up time between 6H00 and 8H00, Daily TST (Total Sleep Time) between 7 and 9 hours, With no strong suspicion of OSAS (Obstructive Sleep Apnea Syndrome) as assessed by STOP-BANG questionnaire, With no suspicion of RLS (Restless Legs Syndrome) as assessed by RLS screening questionnaire, With sufficient reading abilities for the reading task as assessed by ECLA16+ ("Evaluation des Compétences de Lecture chez l'Adulte de plus de 16 ans" :  higher ou equal performances than 25th percentile for performances assessed in total population for the following tasks : " lecture de " l'Alouette " " (Number of correctly read words / minute ≥ 121, number of errors ≤ 10), isolated words reading (regular words : score ≥ 18, time ≤ 17 sec ; irregular words : score ≥ 16, time ≤ 16 sec, pseudo-words : score ≥ 17, time ≤ 26 sec), repetition of non-words (score ≥ 19), and symbol crossing task (number of crossed symbols ≥ 22),  With a SE (Sleep Efficiency) higher or equal to 85% as assessed by the 7 nights-actigraphy made before inclusion, With an AHI (Apnea/Hypopnea Index) lower or equal to 10 apnea or hypopnea/hour of sleep as assessed by the ventilatory polygraphy, With a PLMI (Periodic Limb Movement Index) lower or equal to 15 sequences of PLM/hour of sleep as assessed by the ventilatory polygraphy, Being an affiliated member of the Social Security system, Being able to understand the study, Being available to come at the four visits necessary for the study, Having given written informed consent to participate to the study.  Exclusion Criteria:  Having a life-threatening disease, Any evolutive cardiovascular pathology - under treatment or not, Any evolutive neurologic pathology - under treatment or not (brain tumour, epilepsy, headache, stroke, sclerosis, myoclonia, chorea, neuropathy, muscular dystrophies, myotonic dystrophy), Psychiatric disorders - under treatment or not (characterised depressive episode, bipolar disorders, psychotic disorders, neurodevelopmental diseases), Untreated endocrine disorders (diabetes, hyperthyroidism), Dependency to a substance, otorhinolaryngological disorder that could induce vocal parameters modification, Fluence disorders (cluttering, stuttering), language disorders (dyslexia) or visual troubles that could impact reading abilities, Participant under psychotropic treatment (antidepressants, antihistamine, etc…), or under treatment that could interfere with sleep or wakefulness level, Participant under treatment that could impact the normal muscular function (myorelaxant, neuromuscular blocking agents injections in maxillofacial area, etc…), Dental care during the follow-up of the study, Shift-worker or night-worker, Excessive consumption of alcohol (>2 glasses per day) during the 6 last months, Excessive consumption of coffee, tea, or any drink containing caffeine (like cola) (> 5 cups/day), Excessive tobacco smoking (>5 cigarets/day), Non-native French speaker, Participant with a thick accent that could induce significantly vocal parameters modification (at the discretion of the investigator), Deprived of liberty by a legal or administrative procedure, Under tutorship or guardianship, Pregnant or breastfeeding woman.