Most adults can remember only one or two events before they were four years old and nothing before they were three years old. Children begin to have semantic memories (identifying objects in their environment) by 10 to 12 months, and they appear to develop episodic memories (of things that happened earlier in time) by 20 to 24 months. Young children may be unable to form memories solid enough to survive into adulthood until they can think of their experiences in words.

Studies show that the human sleep cycle is crucial to creating memories. If something important happens to you during the day, your brain strengthens your perceptions of that event overnight while you rest.

Information stored in your memory can be classified according to length: short-term; long-term (or remote); and recent (or working). A short-term memory must be meaningful in some way to make a lasting impression on you. The more connections that exist between that particular memory and your bank of long-term memories, the easier it will be for you to recall it.

Most researchers think that once information has been stored in long-term memory, it is there permanently. However, sometimes we can't find a way to retrieve the information because the link (or association) has faded. Short-term memories fade quickly, sometimes after only a few seconds. Recent, or working, memories are often replaced by incoming information.

Remembering to do something, like run an errand or take daily medication, is called "prospective" memory. Researchers have found that following through on this type of task is related more to a memory trigger, such as seeing a dry cleaning receipt or driving past a pharmacy, than to having the task committed to memory.

Memory problems can be caused by many physical and psychological conditions not related to ageing, including dehydration, infections and stress. Other causes of memory problems include medications, substance abuse, poor nutrition, depression, anxiety and thyroid imbalance.

Some memory loss can occur with age, but not everyone experiences it. People who are more active, both mentally and physically, tend to have better memory function than people who live a sedentary, mentally unchallenging lifestyle.

Studies have shown that older people who are socially active or live with someone tend to maintain better cognitive health.

High blood pressure can affect blood vessels that supply the brain and contribute to memory loss. The reverse also may be true, as studies indicate that aerobic exercise is associated with improved memory.

Mentally challenging activities, such as crossword puzzles and board games, and physical activity, such as brisk walking, may help maintain brain function and preserve memory. One study also suggests that meditation can benefit seniors with memory problems in just eight weeks.

As we age, it can become more difficult to pay attention to more than one thing at a time, so if an older person is distracted by a conversation when he’s parking the car, he may not know where it is later. If you’re having trouble with things like that, make sure your attention is focused when you’re parking the car or putting away your keys so you can find them later.

Memory problems are the hallmark of Alzheimer's disease. In fact, even before patients develop Alzheimer's disease, they often suffer from a condition called mild cognitive impairment (MCI), which includes a greater level of memory loss than is normal for their age. Not all people with MCI go on to develop Alzheimer's disease, however.

Forgetting where you put your keys, forgetting words or names, and taking longer to learn new things are indications of mild forgetfulness, which is common as we age. However, getting lost in places you know well can signal a more serious problem such as Alzheimer's disease, depression, or a blood clot. Other signs of a serious memory problem include asking the same questions repeatedly, not being able to follow directions, becoming confused about time, people, and places, and forgetting to take proper care of yourself.

One study found that older men living with wives with dementia had an almost 12-fold increased risk of developing dementia. Elderly women whose husbands developed dementia had a four times increased risk. Even so, most people in the study did not develop dementia when their spouse did. The stress of being a carer, which has been linked to depression and poorer overall health, may be a factor.