This trial is conducted in Europe. The aim of the trial is to compare cognitive function and associated brain activation patterns during an acute hypoglycaemic episode and during euglycaemia (normal blood glucose concentration). Additionally, the purpose is to assess cognitive function in the recovery phase after hypoglycaemia or euglycaemia, respectively, in subjects with type 1 diabetes.

Inclusion Criteria:

• Right-handed subjects
• Type 1 diabetes mellitus for at least 12 months
• Treated with multiple daily insulin injections or continuous subcutaneous insulin infusion (CSII) for at least 12 months
• Body mass index 18.0-28.0 kg/m^2 (both inclusive)

Exclusion Criteria:

• Subject who has donated any blood or plasma in the past month or more than 500 mL within 3 months prior to screening
• Current tobacco user (any smoking or use of nicotinic products within 3 months prior to screening)
• Visual impairment or auditory impairment