John has been diagnosed with alzheimer's disease. while he is quite forgetful, he is still able to recall events from his teenage and young adult years. that is because his is still intact.

Long-term memories.

Explanation:

Alzhemer´s is a diseases that damages the memories and eventually damages the way in which people beheave, this is because eventually it causes dementia, it´s is a progresive disease meaning that it starts slowly and develops over time, often people start by not being able to remember short term memories, and it slowly develops over time where their long term memories also are forgotten.