Inclusion Criteria:  informed consent obtained age between 18 - 40 male body mass index 18 - 27  Exclusion Criteria:  Age < 18 or > 40 Alcohol Use Disorders Identification Test (AUDIT) >6 points Drug Abuse Screening Test 20 (DAST-20) > 0 points Beck Depression Inventory (BDI) > 11 points Symptom Check List 90 (SCL-90) over mean values of Finnish population in any dimensions of the SCL-90 or the global severity index Any respiratory disorder including sleep apnea Any heart illness Epilepsy Known vitamin B12 deficiency