Amnestic Syndrome: Causes, Symptoms And Main Types
Lesions in the medial temporal lobe cause deficits in anterograde memory, and frequently also in retrograde memory.
In this article we will analyze what amnestic 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.
The concept “amnesic syndrome” has a relatively generic character It is used to refer to any permanent memory impairment that occurs as a result of damage to the brain, so it can include disorders due to very different causes; However, Wernicke-Korsakoff syndrome is the most representative.
Generally, the term “amnestic syndrome” is used to talk about disorders that specifically affect memory, without other cognitive deficits (for example in intelligence or language) being present. If they are, memory problems usually have a clinical significance much greater than the rest.
Consequently, The causes of 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 retrieval of memories, such as the hippocampus and the amygdala, fundamental in spatial and emotional memory respectively.
Types of amnesia: retrograde and anterograde
This type of damage causes the affected person to have severe problems learning new information; This phenomenon is known as anterograde amnesia, and is sometimes, but not necessarily, accompanied by retrograde amnesia, consisting of the forgetting of memories that were encoded before the brain injury.
At a clinical level, patients with amnestic syndrome may manifest apparently normal functioning, since their working memory is not affected, nor is their ability to carry out new procedural learning. However, Deficits in declarative memory 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. As for anterograde amnesia, it is now known that it is not usually as extreme as was thought years ago, since the maintenance of other memory functions makes it possible to compensate for declarative deficits.
Main causes of this disorder
Any factor likely 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 brain tumors.
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 disorders. However, many authors would not consider these effects a true amnestic syndrome because of their transitory nature.
1. Wernicke-Korsakoff syndrome
Wernicke-Korsakoff syndrome is due to deficiencies of vitamin B1, which is also called thiamine The most common cause is malnutrition, especially when it is related to alcohol abuse over a long period of time. This disease consists of two phases: Wernicke’s encephalopathy and Korsakoff syndrome.
During the acute phase, symptoms and signs appear 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 pupils). eye muscles).
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 memories encoded up to two decades before Wernicke’s encephalopathy occurred.
2. Strokes
Heart attacks and hemorrhages in the brain are two very common causes of amnesic syndrome, particularly when they occur in the anterior communicating artery, the anterior cerebral artery, or the Heubner artery. Fabulation or involuntary invention of memories, a characteristic sign of amnestic syndrome is very common in these cases.
Another similar phenomenon that is also associated with amnesia is cerebral anoxia, which consists of the interruption of oxygen supply to this organ as a result 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 close to the limbic system frequently causes amnestic syndrome An especially 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 herpes simplex virus infection and which 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.
