Obesity and especially type 2 diabetes (T2D) increases the risk of neurocognitive dysfunctions including adverse effects on brain structure and function. Recent evidence from clinical studies have shown that T2D almost doubles the risk for dementia. As the population gets older, age-related chronic diseases, as T2D, become more prevalent. Scientific evidence is emerging that there are several links between metabolic and neurocognitive functions. Impaired insulin action (i.e. insulin resistance), the main hallmark of T2D, has been suggested as a likely shared common pathophysiological mechanism. However, the neural processes that determine how insulin resistance is are connected to the onset and progression of T2D and dementia remain unclear. In this context, the overall aim is to study brain insulin resistance to disentangle age-related and obesity related brain insulin resistance in healthy normal and overweight/obese persons at the age of 20 to 70 years . To this end, the investigators will assess brain insulin action using intranasal insulin/placebo during functional Magnetic Resonance Imaging (fMRI). Additionally, structural changes and cognitive processes will be assessed as secondary variables.

Inclusion Criteria:

• Body-Mass Index (BMI) between 19-35 kg/m2
• HbA1c ≤6.0%
• normal glucose tolerance during 75g oral glucose tolerance test (OGTT)

Exclusion Criteria:

• Not removable metal parts in or on the body
• manifest cardiovascular disease
• claustrophobia
• recent surgery (less than 3 months)
• Simultaneous participation in other studies
• Acute disease or infection within the last 4 weeks
• neurological and psychiatric disorders
• treatment with centrally acting drugs
• hemoglobin Hb <13g / dl
• Hypersensitivity to any of the substances used