This is a common question, especially among those over 40 years old. As we age, our brains become electrically less excitable, making it harder to retrieve well-learned information - known as long-term memory - such as the names of people, places and things. It also requires more effort to acquire, store or learn new information - known as short-term memory - such as where the keys were left, what you just bought at the store, and whether you asked a particular question of someone yesterday. Additionally, our "mental scratch pad" - known as working memory - monitors what we are experiencing or attending to at the moment, and holds progressively less information as we age, such that you may not recall why you went into the other room, or what telephone number you were just told to call.
These age-related memory changes routinely cause concern about having Alzheimer's or some other dementing disorder. However, short-term memory is the type first affected by Alzheimer's disease (AD).