Amnestic Disorders Health Article

Definition

Amnestic disorders are conditions that cause memory loss.

Description

Memory is the ability to retain and recall new information. Memory can be subdivided into short-term memory, which involves holding onto information for a minute or less, and long-term memory, which involves holding onto information for over a minute. Long-term memory can be further subdivided into recent memory, which involves new learning, and remote memory, which involves old information. In general, amnestic disorders more frequently involve deficits in new learning or recent memory.

There are a number of terms that are crucial to the understanding of amnestic disorders. In order to retain information, an individual must be able to pay close enough attention to the information that is presented; this is referred to as registration. The process whereby memories are established is referred to as encoding or storage. Retaining information in the long-term memory requires passage of time during which memory is consolidated. When an individual's memory is tested, retrieval is the process whereby the individual recalls the information from memory. Working memory is the ability to manipulate information from short-term memory in order to perform some function. Amnestic disorders may affect any or all of these necessary steps.

The time period affecting memory is also described. Anterograde amnesia is more common. Anterograde amnesia begins at a certain point in time and continues to interfere with the establishment of memory from that point forward in time. Retrograde amnesia refers to a loss of memory for information that was learned prior to the onset of amnesia. Retrograde amnesia often occurs in conjunction with head injury, and may result in erasure of memory of events or information from some time period (ranging from seconds to months) prior to the head injury. Over the course of recovery and rehabilitation from a head injury, memory may be restored or the period of amnesia may eventually shorten.

Demographics

About 7% of all individuals over the age of 65 have some form of dementia that involves some degree of amnesia, as do about 50% of all individuals over the age of 85.

Causes and symptoms

A number of brain disorders can result in amnestic disorders, including various types of dementia (such as Alzheimer's disease), traumatic brain injury (such as concussion), stroke, accidents that involve oxygen deprivation to the brain or interruption of blood flow to the brain (such as ruptured aneurysms), encephalitis, tumors in the thalamus and/or hypothalamus, Wernicke-Korsakoff syndrome (a sequelae of thiamine deficiency usually due to severe alcoholism), and seizures. Psychological disorders can also cause a type of amnesia called "psychogenic amnesia."

A curious condition called transient global amnesia causes delirium (a period of waxing and waning confusion and agitation), anterograde amnesia, and retrograde amnesia for events and information from the several hours prior to the onset of the attack. Transient global amnesia usually only lasts for several hours. Ultimately, the individual recovers completely, with no lasting memory

deficit. The cause of transient global amnesia is poorly understood; researchers are suspicious that it may be due to either seizure activity in the brain or a brief blockage in a brain blood vessel, which causes a brief stroke-like event that completely resolves without permanent sequelae (similar to a transient ischemic attack).

Symptoms of amnestic disorders may include difficulty recalling remote events or information, and/or difficulty learning and then recalling new information. In some cases, the patient is fully aware of the memory impairment, and frustrated by it; in other cases, the patient may seem completely oblivious to the memory impairment or may even attempt to fill in the deficit in memory with confabulation. Depending on the underlying condition responsible for the amnesia, a number of other symptoms may be present as well.