Drug administration
At each experimental night, study participants were awoken at 02:30 a.m. to receive 50 mg/kg of GHB (Xyrem®) or placebo dissolved in 2 dL of orange juice, matched in appearance and taste (see Study design of the experimental nights. Sleep period (23:00–07:00), time point of drug administration (02:30) and MRS/MRI scan (09:00) are indicated.