Retrograde amnesia: definition, symptoms, causes and types.

This type of syndrome caused by alterations in the brain affects memory functioning.

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 discuss what retrograde amnesia is and what its most common causes are. 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 characteristic is selective memory impairment. When the person presents an inability to acquire new information we say that he or she has anterograde amnesia; if memory problems affect pre-disease memories, amnesia is retrograde.amnesia is retrograde.

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

Retrograde amnesia usually affects mainly declarative or explicit memory, including semantic, episodic, and episodic memory. 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 lesion.

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 impairment of the components of 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 in other related structures, both cortical and peripheral. and other related structures, both cortical and subcortical, especially in the temporal lobe. This damage may be due to cranioencephalic trauma, vitamin B1 deficiency due to malnutrition or abusive consumption of toxic substances such as alcohol, among others.

Cases of retrograde amnesia retrograde amnesia of psychogenic origin have also been describedassociated fundamentally to experiences of very intense stress and characteristic of dissociative disorders. Despite the criticisms that the conceptualizations of this type of amnesia have received, its Biological basis is currently being investigated with promising results.

Types of retrograde amnesia

As we have said, the brain lesions 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 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 retained to a greater extent than more recent ones. 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 temporal gradient is not always observed and its intensity is influenced by very different factors, among which the following stand out the location and extent of brain damage. In many cases of Wernicke-Korsakoff syndrome, 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 other hand, others consider that it should be used to refer to cases of functional retrograde amnesia, i.e. those in which there is no brain lesion.

If we stick to the first conceptualization pure retrograde amnesia is associated with lesions in the thalamusThe thalamus, a nucleus of gray matter (composed mainly of neuronal bodies and glial cells) that plays a key role in the retrieval of memories through its connections with the hippocampus, as well as serving as a synaptic relay point.

3. Generalized or global amnesia

Lesions affecting 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 transient amnesic deficits occur due to mild ischemic accidents, intense stress or other causes.

4. Psychogenic amnesia

The concept of "psychogenic amnesia" includes the following 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 widely accepted.

In this regard, the relationship of psychogenic retrograde amnesia with dissociative disorders, including dissociative fugue and dissociative identity disorder, is noteworthy. Psychogenic amnesia is considered the core of this diagnostic category, questioned by many members of the scientific community because of its relationship to suggestion.