Three groups of participants have been included: 7 patients diagnosed with dementia of the Alzheimer's type; 13 patients with mild cognitive impairment due to AD, which represents a preclinical stage of AD in which patients already have memory impairment and at least one AD biomarker (i.e. hippocampal atrophy or abnormal amyloid and tau protein content in the cerebrospinal fluid); and 19 healthy controls. Patients have been recruited from the memory clinics of the Maastricht University Medical Center and the Leiden University Medical Center.