Amnesic syndrome: main causes, symptoms and types

Damage to the medial temporal lobe results in deficits in antegrade memory, and frequently also in retrogradation.

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

What is amnesic syndrome?

The concept of “amnesic syndrome” is relatively generic.. It is used to refer to any permanent memory impairment that occurs as a result of brain damage, so it can include disorders due to very different causes; however, Wernicke-Korsakoff syndrome is the most representative.

In general, the term “amnesic syndrome” is used to designate disorders which specifically affect memory, without other cognitive deficits being present (eg in intelligence or language). If they are, memory problems usually have a much higher clinical significance than others.

Therefore, the causes of amnesic syndrome tend to be focal lesions of the medial areas of the temporal lobe, More precisely in the structures of the limbic system involved in the consolidation and retrieval of memories, such as the hippocampus and the amygdala, fundamental respectively in spatial and emotional memory.

Types of amnesia: retrograde and anterograde

This type of damage causes serious problems for the affected person to learn new information; this phenomenon is known as anterograde amnesia, and is sometimes, but not necessarily, accompanied by retrograde amnesia, consisting of forgetting encoded memories before the brain injury.

At the clinical level, patients with amnesic syndrome may present with apparently normal functioning, as their working memory is not affected, nor their ability to perform new procedural-type learning. However, declarative memory deficits greatly interfere with the lives of these people.

In general, retrograde amnesia is more evident in recent memories than in distant memories, although its severity depends on the injury. As for anterograde amnesia, we know today that it is generally not as extreme as it was thought years ago, because the maintenance of other mnemonic functions makes it possible to compensate for the declarative deficits.

Main causes of this disorder

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

Retrograde amnesia is also one of the most characteristic side effects of electroconvulsive therapy, which is sometimes applied in cases of major depression and bipolar disorder, among other psychological disorders. However, many authors would not consider these effects to be a true amnesic syndrome because of their transient nature.

1. Wernicke-Korsakoff syndrome

Wernicke-Korsakoff syndrome is caused by a deficiency of vitamin B1, also called thiamine. The most common cause is malnutrition, especially when linked to alcohol abuse over a long period. This disease has two phases: Wernicke’s encephalopathy and Korsakoff syndrome.

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

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

2. Strokes

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

Another similar phenomenon which is also associated with amnesia is cerebral anoxia, which involves the disruption of the flow of oxygen to this organ as a result of cardiac arrest; this can lead to the destruction of cells in the hippocampus and other regions of the temporal lobe, which explains the development of memory problems.

3. Tumors of the ventricles

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

4. Herpetic encephalitis

Herpetic encephalitis is a disease of the central nervous system that occurs due to infection with the herpes simplex virus, And it can cause permanent symptoms like amnesia, confusion, and seizures due to damage to the hippocampus, amygdala, uncus and other areas of the limbic system.

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