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 most frequent, and we will describe the four most representative types.

• Related article: "The different types of amnesia (and their characteristics)"

What is retrograde amnesia and what causes it?

The term "amnesia" refers to a neurocognitive syndrome whose defining characteristic is selective memory impairment. When the person presents an inability to acquire new information we say that he has anterograde amnesia; Yes memory problems affect pre-illness memories, amnesia is retrograde.

The two types of amnesia may or may not occur together. Amnesic syndrome, caused by lesions in the medial region of the temporal lobes of the brain such as those that occur in Wernicke-Korsakoff syndrome, it is diagnosed based on the presence of amnesia antegrade; in these cases there is not always a relevant degree of retrograde amnesia.

Retrograde amnesia generally affects the declarative memory or explicit, which includes semantic, episodic, autobiographical and spatial memory. In contrast, procedural or implicit memory is usually preserved in people with this alteration, so they do not forget the skills they had learned before the injury.

In any case, memories are complex phenomena made up of different types of information; This is why, even in cases where there is a dissociation between the affectation of the memory components declarative, it is difficult to differentiate one function from the rest, and therefore to compare the deficits in each of the they.

The main cause of retrograde amnesia is lesions in the hippocampus and in other related structures, both cortical and subcortical, especially the temporal lobe. These damages can be due to head injuries, vitamin B1 deficiency due to malnutrition or abusive consumption of toxic substances such as alcohol, among others.

Cases of retrograde amnesia of psychogenic origin, fundamentally associated with experiences of very intense stress and characteristic of dissociative disorders. Despite the criticism that conceptualizations about this type of amnesia have received, its biological bases are currently being investigated with promising results.

• You may be interested: "What is anterograde amnesia and what symptoms does it have?"

Types of retrograde amnesia

As we have said, the brain lesions that cause 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 temporal gradient

Retrograde amnesia often has a clear temporal gradient: memories of the remote past tend to be preserved to a greater extent than the most recent ones. 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 temporal gradient is not always observed and its intensity is influenced by very different factors, among which are the location and extent of brain damage. In many cases the Wernicke-Korsakoff syndromeAs a prototypical example of amnesic 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 anterograde amnesia, regardless of its cause; on the contrary, 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 retrieval of memories through its connections with the hippocampus, in addition to serving as a synaptic relay point.

• You may be interested: "Thalamus: anatomy, structures and functions"

3. Generalized or global amnesia

Lesions affecting memory areas of the brain 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 transient memory deficits due to mild ischemic attacks, intense stress, or other causes.

4. Psychogenic amnesia

The concept "psychogenic amnesia" includes the retrograde memory disturbances caused by psychological factors. From different theoretical orientations, these cases have been attributed to traumatic and / or intensely stressful experiences; anxiety can alter the encoding of information, although the repression of memories is not so accepted.

In this sense, it is worth highlighting the relationship of psychogenic retrograde amnesia with dissociative disorders, which include dissociative fugue and dissociative identity disorder. Psychogenic amnesia is considered the nucleus of this diagnostic category, questioned by many members of the scientific community for its relationship with suggestion.