Drug administration
A subanesthetic dose of ketamine was delivered via a Graseby 3500 intravenous infusion pump controlled by the STANPUMP software (Steven Shafer, M.D., Anesthesiology Service, PAVAMC 3801 Miranda Ave., Palo Alto, USA). Target plasma levels were 100 ng/ml with an initial bolus administered as a 2 mg/ml solution. The plasma level of 100ng/ml was chosen in accordance with a study of Krystal et al.