The goal of this study is to better understand the relationship between peripheral and central nervous system measurements of the gamma-aminobutyric acid (GABA) system in otherwise healthy individuals. the main questions it aims to answer are:

1. Does GABA cross the blood-brain barrier?
2. Can peripheral measurements of the GABAergic system be used to study GABA in the brain?

Participants will receive oral GABA and Placebo and undergo blood draws, MRI scans and transcranial magnetic stimulation sessions.

Although gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the central nervous system in humans, and various pharmacological compounds and natural products aim to modulate it, it is still unknown whether GABA can cross the blood-brain barrier. The present project aims to clarify this issue by comparing measurements obtained in the central nervous system (the brain) with peripheral measurements (serum) following oral administration of the amino acid GABA. This will help determine if peripheral concentrations of GABA in the blood reflect levels in the brain. This would facility studying the GABAergic system in vulnerable clinical populations (such as children or patients with intellectual disabilities) to participate in without resorting to expensive neuroimaging exams and the inclusion of individuals who cannot undergo neuroimaging exams (e.g., claustrophobia, presence of metal in the body). To achieve this, GABA measurements (serum and neuroimaging) will be obtained before and after the oral intake of 1800mg of GABA or a placebo in 30 healthy adults participating in a cross-over, single-blind study with repeated measures.

Inclusion Criteria:

• Be between 18 and 35 years old
• Be of right manual dominance
• In good health

Exclusion Criteria:

• Have an implant or pacemaker,
• Having tinnitus,
• Have a history of fainting,
• Have already had an epileptic seizure or have a family history of epilepsy,
• Have a known neurological disease,
• Have a diagnosis of diabetes
• Be under psychotropic medication,
• Have suffered from substance abuse or dependence in the last 6 months,
• Have a neurostimulator,
• Have a splinter or metallic implant in the head or the rest of the body,
• Have a cochlear implant,
• Have an automated injection system implanted (insulin pump),
• Have a transdermal patch,
• Have tattoos in the area to be studied,
• Be pregnant or breastfeeding,
• Being claustrophobic or having other reasons that would prevent the volunteer from tolerating the imaging exam.

The research team will conduct the randomization and participant code allocation process using REDCap and will dispense the medication or placebo based on the randomization. The placebo will be visibly identical to that of the active medication (i.e. white powder in a gel capsule of the same size and colour as the active medication)