Abstract: Studies conducted in recent 10 years to study the cognitive impairments of patients with type 2 diabetes were reviewed. It was confirmed that hyperglycemia can cause cognitive problem, although inconsistent conclusions still remain. Some studies found impairment while the others didn’t. So far, most studies confirmed the impairment of learning and memory function in patients with type 2 diabetes. Cognitive threshold theory was used to explain the remain controversy, by which only the patients aged from 60 to 70 will display impairment compared with the controls. Reduced level of insulin in central nerves system was also studied. Reasons of cognitive impairment and more sensitive measurements were suggested

Key words: Non-Insulin Dependent Diabetes Mellitus, cognitive ageing, Threshold theory on cognition pairment