The present invention provides a use of an insulin for the manufacture of a medicament for treating or preventing diseases or disorders of adult brain. Also provided is a method for treating or preventing diseases or disorders of adult brain by administering an effective amount of an insulin to the brain. The diseases or disorders of adult brain are associated with tissue shrinkage or atrophy. The amount of the insulin administered is preferably from 0.001 Units per kg body weight per day up to 10 Units per kg body weight per day.