Progressive losses in adaptive learning capability and cognitive function beyond what might be expected from normal aging. Although it is most common among the elderly, dementia can occur in adults of any age.
Some symptoms include: difficulty being able to remember recent events, not remembering people and places from your life, difficulty finding the correct words to express what you are thinking or even to name objects, issues with completeing tasks fully (cooking from a recipe, balancing your checkbook etc), depression and a tendency to stop exercising personal care regimines (bathing, grooming etc). For a full list of symptoms and a more in-depth description of this issue, please visit: http://www.webmd.com/alzheimers/tc/dementia-symptoms
Example: A college student sustains a head injury. He recovers enough to drive a taxi, but will never again be able to master academic material.