Alzheimer's Disease (AD) is the most common form of dementia and may contribute to 60-70 % of all cases. An early, accurate diagnosis of AD will become increasingly important with disease-modifying therapies. Different types of fluid and neuroimaging biomarkers are available for the early detection of AD. However, implementation of routine use of these biomarkers in clinical settings is held back due to the risk of overdiagnosis, increased cost and invasiveness of the assessment method. Therefore, novel biomarkers are needed beyond the amyloid and tau pathologies for the early diagnosis of AD. Neuropsychological paper and pencil tests can detect AD and discriminate between different clinical stages. Since medial temporal lobe structures, including the hippocampus and entorhinal cortex (EC), are involved in spatial navigation and degenerate in the earliest stages of AD, spatial navigation can be considered as an early cognitive biomarker of the disease. Nonetheless, the measurement of spatial navigation needs further improvement since the current paper and pencil tests lack ecological validity. Therefore, the test environment should be set up in immersive Virtual Reality (iVR). Dr. Andrea Castegnaro (Space and Memory Lab of University College of London) developed the Allocentric Spatial Update Task (ALLO task), which is an iVR task measuring egocentric and allocentric spatial abilities. Therefore, the main objective of this study is to evaluate whether allocentric and egocentric spatial navigation, measured by the ALLO iVR task can be considered a cognitive biomarker for the early detection of AD. In addition, the investigators want to report on the neuronal correlates of both spatial navigation strategies. Through the Department of Neurology of the University Hospital of Ghent, which has a large cognitive disorders clinic, patients with mild cognitive impairment and mild Alzheimer's dementia will be recruited. Participants will undergo standard clinical assessment, including a neuropsychological examination, Magnetic Resonance Imaging, a 18F-fluorodeoxyglucose PET and a Lumbar Puncture. In addition, participants will also be asked to undergo Tau PET imaging, Amyloid PET imaging and complete the ALLO iVR task. Healthy controls will also be recruited and have to undergo the same investigations, except for the amyloid PET and lumbar puncture.