The investigators will investigate the effect of hypobaria and hypoxia on physiological responses such as: oxygen saturation, heart rate, cerebral blood flow, cerebral oxygenation, brain's activity and concentration performance.

The main goal of this project is to investigate how hypoxia affects cognitive functions. The KLT-R test asses the concentration level of a person. Subjects will do this test at different simulated altitude level in the hypobaric chamber at the FAI in Dübendorf. Investigators' first hypothesis is that concentration level will be altered by hypoxia. The higher altitude the subjects are, the more the concentration would be altered. KLT-R performance would be impaired by hypoxia compare to sea level performance.

The primary endpoint of this project is to investigate how KLT-R performance is affected by the different hypoxic conditions. KLT-R test will be passed nine times in total during the test visit. There will be a pre-test; a test at each of the conditions (3000m HH, 5500m HH, 5500m NH and 5500m HN); between each condition at sea level (to have a new baseline before each condition) and a post-test at the end of the protocol. To avoid influence of fatigue, all conditions will be randomized.

The second endpoint of this study is how the brain electrical activity is modulated by hypoxia. Micro-states also will be measure during hypobaric hypoxia conditions (3000m HH and 5500m HH).

Inclusion Criteria:

• No history of flight sickness
• No relevant medical diseases
• Age 18 - 40 years
• Written consent acceptance

Exclusion Criteria:

• Known pathologies
• Relevant medical disorders
• Drug addiction
• Anemia or poor health
• People who have already had problems with elevation

Results will be shared in scientific publications by the end of this year and in 2018.