The Effect of Ketamine on Attentiveness

Inclusion Criteria: * Normal ECG and safety assessments, or minor no-relevant deviations, at screening * Vital signs: systolic between 100 and 140 mmHg and diastolic between 50 and 90 mmHg and heart rate between 45 and 90 beats/min * No medication intake in the last four weeks * Volunteers must have signed an informed consent document indicating that they understand the purpose of and procedures required for the study and are willing to participate in the study and to adhere to the prohibitions and restrictions specified in the protocol * Negative drug screen Exclusion Criteria: * Participation in another clinical trial in the last 3 months * Significant allergies, allergic diathesis or known hypersensitivity for ketamine or its ingredients (ie, Benzethonium chloride) * History of or current significant respiratory disease, cardiovascular disease, endocrinological, gastrointestinal, neurological, glaucoma and known liver and kidney failure * Contraindications for an MRI being performed (claustrophobia, metal parts, pacemaker) * oxygen saturation pO2 \< 90 mmHg * Clinically significant abnormalities in ECG or laboratory values * Recent history (within previous 6 months) of alcohol or drug abuse * History of or current psychiatric diagnoses (DSM-IV, II) or neurological disorders * Relatives in first or second degree with a schizophrenic disorder * Serology positive for hepatitis B surface antigen, hepatitis C antibodies or HIV antibodies * Signs of hyperthyroidism based on the determination of T3, T4 and TSH