Gut bacteria byproducts may tame inflammation and shield the brain

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Voluntary written informed consent obtained prior to any study procedure * Healthy, with no gastrointestinal or psychological complaints * Age 18-45 years * BMI 18.5-27 kg/m2 * Proficiency in English and/or Dutch Exclusion Criteria: * History of previous or current neurological disorder (e.g., epilepsy, multiple sclerosis, migraine with aura) * History of previous or current psychiatric disorder (e.g., depression, anxiety disorders, bipolar disorder, schizophrenia) * History of previous or current gastrointestinal disorder (e.g., Crohn's disease, ulcerative colitis, irritable bowel syndrome) * History of previous or current endocrine disorder (e.g., diabetes, thyroid disorders, polycystic ovary syndrome) * History of immune system disorder, including inflammatory, autoimmune, or severe allergic conditions (e.g., rheumatoid arthritis, lupus, celiac disease, or severe allergies such as anaphylaxis) * History of neuropsychiatric disorder (e.g., ADHD, autism spectrum disorder, learning disorder, Tourette's syndrome) * History of major head trauma (e.g., concussion with loss of consciousness or long-term symptoms) * History of severe infection (e.g., sepsis, pneumonia requiring hospitalization, meningitis, endocarditis, or other systemic infection requiring hospitalization, intravenous antibiotics, or intensive care) * One or more diagnoses based on the Mini International Neuropsychiatric Interview (MINI) * One or more diagnoses based on ROME-IV criteria for gastrointestinal disorders * Any disorder that, in the investigator's opinion, might jeopardise the participant's safety or compliance with the protocol * Any prior or concomitant treatment that might jeopardise the participant's safety or compromise the integrity of the study * Participation in an interventional trial with an investigational medicinal product (IMP) or device * Current or recent (past month) prescribed medication use, with particular attention to cardiovascular drugs, steroids, NSAIDs, and centrally-acting drugs (excluding isolated over-the-counter use such as ibuprofen or paracetamol, and hormonal contraceptives in women) * Use of psychotropic medication within the past year (e.g., antidepressants, anxiolytics, antipsychotics) * Use of antibiotics within three months preceding the study * Use of pre- or probiotics within one month preceding the study * Current or recent (past month) infection (e.g., common cold, influenza, COVID-19) * Recent (past month) vaccination * Pregnant or lactating women * Previous or current substance or alcohol dependence or abuse (\>2 units/day or \>14 units/week) * Smoking * Night-shift work * Adherence to special diets (e.g., vegan, vegetarian, weight-loss, lactose-free, gluten-free) * Previous experience with or knowledge of any of the cognitive tasks used in the study (questionnaires excluded) * C-reactive protein higher than 0.5mg/dL on the day of the injection. * Colour vision deficiency or colour-blindness