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 retrograde amnesia is and what its causes are most frequent, and we will describe the four most representative types.
The term “amnesia” refers to a neurocognitive syndrome whose defining characteristic is the selective impairment of memory. When the person has an inability to acquire new information we say that they have anterograde amnesia; Yeah memory problems affect memories prior to the disease amnesia is retrograde.
The two types of amnesia may or may not occur together. Amnestic 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 anterograde amnesia; In these cases there is not always a relevant degree of retrograde amnesia.
Retrograde amnesia generally affects declarative or explicit memory, which includes semantic, episodic, autobiographical and spatial memory On the other hand, 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 in which 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 compare the deficits in each of them.
The main cause of retrograde amnesia is damage to the hippocampus and in other related structures, both cortical and subcortical, especially the temporal lobe. These damages may be due to head trauma, vitamin B1 deficiency due to malnutrition or abusive consumption of toxic substances such as alcohol, among others.
Cases have also been described of retrograde amnesia of psychogenic origin, fundamentally associated with experiences of very intense stress and characteristic of dissociative disorders. Despite the criticism that the conceptualizations of this type of amnesia have received, its biological bases are 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 frequently associated with the presence of anterograde amnesia. This criterion is one of the most relevant in the classification of retrograde amnesias, along with the causes of the alteration and the specific characteristics of the deficits.
1. With time gradient
Retrograde amnesia often has a clear temporal gradient: Memories of the distant 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 stand out the location and extent of brain damage In many cases of Wernicke-Korsakoff syndrome, a prototypical example of the amnesic syndrome, retrograde amnesia can extend up to 20 years before the onset of the disease.
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, 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 (mainly composed of neuronal bodies and glial cells) that plays a key role in the retrieval of memories through its connections with the hippocampus, in addition to serving as a synaptic relay point.
3. Generalized or global amnesia
Lesions affecting brain areas 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 temporary memory deficits occur 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 as widely accepted.
In this sense, it is worth highlighting the relationship between psychogenic retrograde amnesia and dissociative disorders, which include dissociative fugue and dissociative identity disorder. Psychogenic amnesia is considered the core of this diagnostic category, questioned by many members of the scientific community due to its relationship with suggestion.
