Table 1 Inclusion and exclusion criteria

• Age ≥ 18 and ≤ 35 years

• Healthy individual

• BMI ≥ 18 kg/m² and ≤ 30 kg/m²

• Normal electrocardiogram (ECG)

• Normal physical examination, including neurological examination, auscultation of the heart and lungs, and measurement of blood pressure and pulse

• American Society of Anaesthesiologists (ASA) class 1 [44]

• Mallampati I-II and simplified airway risk index (SARI) 0–2 (i.e. no indication of difficult intubation). See Tables 2 and 3 for details

• Right-handed

• Female participants must use safe contraceptives (hormonal or mechanical, including IUDs)

• Speaks and understands Danish

• Provides oral and written informed consent

• Contraindications to MRI (as described below)

• Left-handedness or ambidexterity.

• History of complications to general anaesthesia, including malignant hyperthermia

• Family history of malignant hyperthermia

• Known incident of malignant hyperthermia or any unexplained complication to general anaesthesia among close relatives

• Allergy to any kind of medication or material to which the volunteer could be exposed during this study

• History of serious illness

• History of cancer, immune disease, autoimmune disease, chronic pain or psychiatric illness

• History of neurological disease with permanent neurological deficits or ongoing neurodegeneration

• Major trauma or head trauma with any symptoms present at the time of inclusion

• Surgery less than 6 weeks prior to the study period

• Infection (with fever) less than 2 weeks prior to or during the study sessions

• Daily use of any medication (not counting contraceptives)

• Consumed anti-depressants during the last 30 days before study days

• Weekly intake of > 21 (for women > 14) units of alcohol

• Heavy intake of caffeine (>  5 cups/day)

• Smoking during the last 30 days before study days

• Substance misuse (assessed by the investigator)

• Pregnancy

• Reflux or dyspepsia

• Poor dental status or oral health

• Expected or suspected difficult airway

• Declines receiving information regarding accidental pathological findings during MRI scans of the brain

• Cannot cooperate to tests

• Otherwise judged unfit for participation by the investigator

Exclusion criteria during the study (leading to withdrawal)

• Any of the above-mentioned exclusion criteria

• Major trauma or head trauma during the study period

• Surgery during the study period

• Infection (with fever) during the study period

• Consumption of more than 3 units of alcohol within 24 h before each study day (intervention day or MRI scan day)

• Consumed analgesics within 3 days before each study day

• Consumed anti-histamines less than 48 h before each study day

• Intake of caffeine 12 h prior to each study day

• Smoking