Retrograde amnesia consists of the loss of memories prior to a brain injury or, depending on some perspectives, relating to experiences of intense anxiety and stress.

In this article we will analyze what is retrograde amnesia and what are its most frequent causes , and we will describe the four most representative types.

What is retrograde amnesia and what causes it?

The term “amnesia” refers to a neurocognitive syndrome whose defining feature is the selective involvement of memory. When the person presents an inability to acquire new information we say that they have antegrade amnesia; if the memory problems affect memories prior to the illness , the amnesia is retrograde.

The two types of amnesia may or may not occur together. Amnesia syndrome, caused by lesions in the medial region of the temporal lobes of the brain such as those found in 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.

Retrograde amnesia usually 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 they do not forget the skills they had learned before the injury.

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

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

Cases of retrograde amnesia of psychogenic origin have also been described, fundamentally associated with experiences of very intense stress and characteristic of dissociative disorders. Despite criticism of the conceptualizations of this type of amnesia, its biological basis is currently being investigated with promising results.

Types of retrograde amnesia

As we have said, the brain injuries that cause most cases of retrograde amnesia are often associated with the presence of anterograde amnesia. This criterion is one of the most relevant in the classification of retrograde amnesia, together with the causes of the alteration and the specific characteristics of the deficits.

1. With time gradient

Retrograde amnesia often has a clear time gradient: memories of the distant past tend to be retained to a greater extent than more 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 time gradient is not always observed and its intensity is influenced by very different factors, among which the location and extent of brain damage stand out. In many cases of Wernicke-Korsakoff syndrome, a prototypical example of amnesia 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; in contrast, others consider that it should be used to refer to functional retrograde amnesia cases, 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 grey substance (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.

3. Widespread or global amnesia

Injuries that affect the 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 temporary mnestic deficits due to mild ischemic accidents, intense stress or other causes.

4. Psychogenic amnesia

The concept “psychogenic amnesia” includes the alterations of the 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 codification of information, although the repression of memories is not as accepted.

In this regard, the relationship of psychogenic retrograde amnesia with dissociative disorders, which include dissociative flight and dissociative identity disorder, should be highlighted. Psychogenic amnesia is considered the core of this diagnostic category, which is questioned by many members of the scientific community because of its relationship with suggestion.