Overview of Memory & Memory Loss

Memory can be defined as the registration, retention, and recollection of experiences, thoughts, feelings, sensations, ideas, and knowledge. Human memory is complex.

Our brains need to remember important facts, future plans, vocabulary words, social norms, and how to perform routine tasks like making breakfast or following a bus schedule. To accomplish all this, the brain sorts through information, evaluates the importance of the information, stores away the information, and then retrieves it when we need it, often within seconds.

Memory problems can affect some or all of these processes. Some memory problems develop slowly, while others occur suddenly. Some types of memory problems are reversible, and others result in a gradual, permanent decline in memory.

Types of Memory Problems

A certain degree of memory loss occurs normally with age. During a person's twenties, brain cells begin dying off gradually and the body starts producing smaller amounts of the chemicals needed for memory function. However, these changes do not affect a person's ability to lead a normal life and any resulting memory loss does not worsen noticeably over time.

There are several types of memory problems that interfere with a person's ability to perform day-to-day tasks. Amnesia, sometimes called amnestic syndrome, impairs a person's ability to remember facts, events, experiences, and personal information. In some cases, difficulty remembering new information also may occur. Usually, the person's general knowledge, focus, intelligence, judgment, language skills, and personality are not impaired, and the person is aware that he or she has the condition.

Transient global amnesia is a complete, but temporary, loss of memory. Most people with this type of memory loss regain their memory within 1 or 2 days.

A person with anterograde amnesia can remember events in the distant past, but not the recent past. The person usually has difficulty learning new things and cannot form new memories. This type of memory loss often results from trauma. Retrograde amnesia affects the ability to remember events that happened before a trauma.

Patients with psychogenic or dissociative amnesia cannot remember who they are. Usually this type of amnesia is triggered by a severely stressful situation and is not permanent.

Mild cognitive impairment (MCI) involves memory loss that is more severe than what is considered normal for the aging process. In MCI, there is measurable memory loss, but that loss does not interfere with a patient's everyday life and is not severe enough to be diagnosed as dementia. In many cases, memory loss in people with MCI does worsen, however, and studies suggest that approximately 12–15% of people with MCI eventually develop Alzheimer's disease. Mild cognitive impairment can also affect a person's language ability, judgment, and reasoning.

Dementia is a condition that causes memory loss that interferes with a person’s ability to perform everyday tasks. In dementia, memory becomes impaired, along with other cognitive skills, such as language use, judgment, and awareness. The most common type of dementia is Alzheimer's disease. Other forms include frontotemporal dementia (sometimes called Pick's disease), Lewy Body dementia, vascular dementia, and mixed dementia.

Incidence and Prevalence of Memory Problems

Incidence and prevalence of memory problems varies and depends on the type. Amnesia is a relatively rare condition. It is estimated that approximately 20% of people over the age of 70 have mild cognitive impairment.

According to Alzheimer's Disease International, approximately 30 million people worldwide suffer from dementia and about two-thirds of these people live in developing countries. In people younger than 65 years of age, dementia affects about 1 person in 1000. In people over the age of 65, the rate is about 1 in 20, and about 1 in 5 people over age 80 have dementia. According to the National Institute of Aging, between 2.4 and 4.5 million people in the United States have Alzheimer's disease.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 29 Dec 2008

Last Modified: 16 May 2011