Amnesic syndrome: causes, symptoms and main types

Injuries to the temporal lobe medial causes deficits in antegrade memory, and frequently also in retrograde memory.

In this article we will analyze what amnesic syndrome consists of and what its main causes are, including the most common and characteristic: Wernicke-Korsakoff syndrome, which is due to malnutrition and alcohol abuse.

What is amnesic syndrome?

The concept "amnesic syndrome" is relatively generic.. It is used to refer to any permanent memory alteration that occurs as a consequence of damage to the brain, which may include disorders due to very different; however, Wernicke-Korsakoff syndrome is the most representative.

In general, the term "amnesic syndrome" is used to refer to disorders that specifically affect the memory, without other cognitive deficits being present (for example in intelligence or language). If they are, memory problems usually have a much higher clinical significance than the rest.

In consecuense, the causes of amnesic syndrome tend to consist of focal lesions of the medial areas of the temporal lobe

, specifically in the structures of the limbic system involved in the consolidation and recovery of memories, such as the hippocampus and the amygdala, fundamental in spatial and emotional memory respectively.

Types of amnesia: retrograde and antegrade

This type of damage causes the affected person to have severe problems learning new information; This phenomenon is known as anterograde amnesia, and it is accompanied sometimes, but not necessarily, due to retrograde amnesia, consisting of forgetting memories that were encoded before the injury cerebral.

Clinically, patients with amnesic syndrome may manifest apparently normal functioning, since their working memory is not affected, nor is their ability to carry out new learning of the type procedural. However, declarative memory deficits greatly interfere with the lives of these people.

Retrograde amnesia is generally more evident for recent memories than for distant ones, although its severity depends on the injury. Refering to anterograde amnesiaNowadays, it is known that it is not usually as extreme as was thought years ago, since the maintenance of other mnemic functions makes it possible to compensate for declarative deficits.

Main causes of this disorder

Any factor capable of damaging the medial temporal regions of the brain has the potential to cause an amnesic syndrome. The most common causes are Wernicke-Korsakoff syndrome, which is associated with excessive consumption of alcohol, herpetic encephalitis and anoxia, as well as heart attacks, hemorrhages and tumors in the brain.

The retrograde amnesia It is also one of the most characteristic side effects of electroconvulsive therapy, which is occasionally applied in cases of major depression and bipolar disorder, among other disorders psychological. However, many authors would not consider these effects a true amnesic syndrome because of their transience.

1. Wernicke-Korsakoff syndrome

Wernicke-Korsakoff syndrome is due to deficiencies of vitamin B1, which is also called thiamine. The most frequent cause is malnutrition, especially when it is related to alcohol abuse for a long period of time. This disease has two phases: Wernicke's encephalopathy and Korsakoff's syndrome.

During the acute phase, symptoms and signs appear such as attention problems, confusion, temporal, spatial and personal disorientation, apathy, pain neuropathic, ataxia (lack of motor coordination in general) nystagmus (involuntary movements of the pupils) and ophthalmoplegia (paralysis of the muscles of the the eyes).

The term “Korsakoff syndrome” refers to the chronic phase of this process, in which severe alterations appear in anterograde and retrograde memory; in the latter case, forgetting usually affects coded memories up to two decades before Wernicke encephalopathy occurred.

2. Strokes

Heart attacks and hemorrhages in the brain are two very common causes of amnesic syndrome, in particular when they occur in the anterior communicating artery, in the anterior cerebral artery or in the artery of Heubner. The involuntary fabrication or invention of memories, a characteristic sign of amnesic syndrome, is very common in these cases.

Another similar phenomenon that is also associated with amnesia is cerebral anoxia, which consists in the interruption of the supply of oxygen to this organ as a consequence of cardiac arrest; This can cause cells in the hippocampus and other regions of the temporal lobe to be destroyed, which explains the development of memory problems.

3. Tumors in the ventricles

The development of tumors in areas close to the limbic system frequently causes the amnesic syndrome. A particularly noteworthy case is that of tumors in the third ventricle, which usually damage the fornix, the main connection between the thalamus and the structures involved in memory.

4. Herpetic encephalitis

Herpetic encephalitis is a disease of the central nervous system caused by a herpes simplex virus infection, and that it can cause permanent symptoms such as amnesia, confusion and seizures due to lesions in the hippocampus, the amygdala, the uncus and other areas of the limbic system.