Retrograde amnesia: definition, symptoms, causes and types
Retrograde amnesia consists of the loss of memories prior to a brain injury or, according to some perspectives, related to experiences of intense anxiety and stress.
In this article we will analyze what is retrograde amnesia and what are its causes more frequent, and we will describe the four most representative types.
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What is retrograde amnesia and what causes it?
The term "amnesia" refers to a neurocognitive syndrome whose defining characteristic is the selective involvement of memory. When the person has an inability to acquire new information we say that he has anterograde amnesia; yes Memory problems affect memories prior to the disease , amnesia is retrograde.
The two types of amnesia can occur jointly or not. The amnestic syndrome, caused by lesions in the medial region of the temporal lobes of the brain such as those that occur in the Wernicke-Korsakoff syndrome, is diagnosed based on the presence of antegrade amnesia; in these cases there is not always a relevant degree of retrograde amnesia.
In general, retrograde amnesia affects mainly declarative or explicit memory, which includes semantic, episodic, autobiographical and spatial memory . In contrast, procedural or implicit memory is usually preserved in people with this disorder, so do not forget the skills they had learned before the injury.
In any case, memories are complex phenomena composed of different types of information; that is why, even in cases where there is a dissociation between the involvement of the components of declarative memory, it is difficult to differentiate one function from the rest, and therefore compare the deficits in each of them.
The main cause of retrograde amnesia are lesions in the hippocampus and in other related structures, both cortical and subcortical, especially the temporal lobe. These damages can be due to traumatic brain injuries, vitamin B1 deficiency due to malnutrition or abusive consumption of toxic substances such as alcohol, among others.
Cases have also been described retrograde amnesia of psychogenic origin , associated mainly with experiences of intense stress and characteristic of dissociative disorders. Despite the criticisms that conceptualizations about this type of amnesia have received, their biological bases are currently being investigated with promising results.
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Types of retrograde amnesia
As we have said, the brain lesions that cause the most cases of retrograde amnesia are frequently associated with the presence of anterograde amnesia. This criterion is one of the most relevant in the classification of retrograde amnesias, together with the causes of the alteration and the specific characteristics of the deficits.
1. With a temporary gradient
Frequently retrograde amnesia has a clear time gradient: memories of the remote past tend to be preserved to a greater extent than the most recent This has been attributed to the fact that the nervous system requires a long period of time to consolidate a memory definitively through the formation of cortical connections.
This temporary gradient is not always observed and its intensity is influenced by very different factors, among which stand out the location and extent of brain damage . In many cases, Wernicke-Korsakoff syndrome, a prototypical example of amnestic syndrome, retrograde amnesia can extend up to 20 years before the onset of the disease.
2. Pure retrograde amnesia
Some authors use the term "pure retrograde amnesia" when this alteration occurs in the absence of antegrade amnesia, regardless of its cause; on the other hand, others consider that it should be used to refer to cases of functional retrograde amnesia, that is, those in which there is no brain injury.
If we stick to the first conceptualization Pure retrograde amnesia is associated with lesions in the thalamus , a nucleus of gray matter (composed mainly of neuronal bodies and glial cells) that has a key role in the recovery of memories through its connections with the hippocampus, in addition to serving as a synaptic relay point.
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3. Generalized or global amnesia
Lesions that affect areas of the brain involved in memory tend to cause both retrograde and anterograde amnesia; When this happens we speak of generalized amnesia. A special case is transient global amnesia, in which there are passenger mnemonic deficits due to mild ischemic accidents, intense stress or other causes.
4. Psychogenic amnesia
The concept of "psychogenic amnesia" includes alterations of retrograde memory caused by psychological factors . From different theoretical orientations these cases have been attributed to traumatic and / or intensely stressful experiences; Anxiety can alter the coding of information, although the repression of memories is not so accepted.
In this regard, the relationship between psychogenic retrograde amnesia and dissociative disorders, which include dissociative fugue and dissociative identity disorder, should be highlighted. Psychogenic amnesia is considered the core of this diagnostic category, questioned by many members of the scientific community for its relationship with suggestion.