Amnestic syndrome: causes, symptoms and main types
Lesions in the medial temporal lobe cause deficits in the antegrade memory, and frequently also in retrograde memory.
In this article we will analyze what the amnestic syndrome consists of and what its main causes are, including the most common and characteristic: the Wernicke-Korsakoff syndrome, which is due to malnutrition and alcohol abuse.
What is amnestic syndrome?
The concept "amnestic syndrome" has a relatively generic character . It is used to refer to any permanent alteration of memory that occurs as a result of damage to the brain, so that it may include disorders due to very different causes; however, the Wernicke-Korsakoff syndrome is the most representative.
In general, the term "amnestic syndrome" is used to talk about disorders that specifically affect memory, without other cognitive deficits being present (for example in intelligence or language). If they are, the memory problems usually have a clinical significance much higher than the rest.
In consecuense, the causes of the amnestic 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 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 to learn new information; This phenomenon is known as antegrade amnesia, and is sometimes, but not necessarily, accompanied by retrograde amnesia, consisting of forgetting memories that were coded before the brain injury.
At a clinical level, patients with amnestic syndrome can manifest an apparently normal functioning, since their operative memory is not affected, nor is their capacity to perform new procedural learning. But nevertheless, deficits in declarative memory greatly interfere in the lives of these people .
In general, retrograde amnesia is more evident for recent memories than for distant memories, although its severity depends on the injury. As for antegrade amnesia, it is now known that it is not usually as extreme as it was thought years ago, since the maintenance of other memory functions compensates for declarative deficits.
Main causes of this disorder
Any factor liable to damage the medial temporal regions of the brain has the potential to cause an amnestic 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 tumors in the brain.
Retrograde amnesia 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 psychological alterations. However, many authors would not consider these effects a true amnestic syndrome because of its transience.
1. Wernicke-Korsakoff syndrome
Wernicke-Korsakoff syndrome is due to deficits of vitamin B1, which is also called thiamin . The most frequent cause is malnutrition, especially when it is related to alcohol abuse over a long period of time. This disease consists of two phases: Wernicke encephalopathy and Korsakoff syndrome.
During the acute phase, symptoms and signs appear as attention problems, confusion, temporary, 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 muscles of the eyes).
The term "Korsakoff syndrome" refers to the chronic phase of this process, in which there are severe alterations in the antegrade and retrograde memory; in the latter case, forgetfulness usually affects memories coded up to two decades before Wernicke's encephalopathy occurred.
2. Cerebrovascular accidents
Heart attacks and hemorrhages are two very common causes of amnestic syndrome, particularly when they occur in the anterior communicating artery, in the anterior cerebral artery, or in the Heubner artery. Fabulation or involuntary invention of memories, a characteristic sign of amnestic syndrome , it is very common in these cases.
Another similar phenomenon that is also associated with amnesia is cerebral anoxia, which consists of interrupting the oxygen supply 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 appearance of memory problems.
3. Tumors in the ventricles
The development of tumors in areas near the limbic system often causes the amnestic 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 that occurs because of an infection of the herpes simplex virus , and that can cause permanent symptoms such as amnesia, confusion and epileptic seizures due to lesions in the hippocampus, amygdala, uncus and other areas of the limbic system.
