RETROGRADE AMNESIA: CHARACTERISTICS, CAUSES AND AREAS INVOLVED - NEUROPSYCHOLOGY - 2024

The retrograde amnesia is a disorder that causes loss of information prior to a specific event. Said memory loss can be partial or total. It appears at specific moments and is defined as a loss of memory of the aspects that have occurred prior to the appearance of the alteration.

The person who suffers from it is unable to recover his memories about past events. Said memory loss is variable, so it can constitute gaps on specific aspects or an inability to remember important and past elements.

The causes are usually diverse, so in each case they can be caused by different factors. The brain areas mainly affected are the basal ganglia, hippocampus and diencephalon.

Features of retrograde amnesia

Retrograde amnesia is a specific type of amnesia. In fact, it refers to the primary cataloging of the modes of presentation of amnesia: retrograde (loss of past information) and anterograde (loss of future information).

Amnesia is defined as the total or partial loss of memory and presents a great heterogeneity of syndromes.

Amnesic syndromes can be found in various pathologies and appear both progressively and abruptly. Likewise, they are temporary or permanent.

Retrograde amnesia, on the other hand, can also occur both acutely and abruptly, although the latter is usually more common.

Likewise, there is no time limit on memory loss. In this way, retrograde amnesia can cause loss of information minutes, hours or even days, months or years prior to the event.

Retrograde amnesia is caused by a certain brain damage or condition. The particularities and intensity of said damage is usually the factor that modulates the quality of memory loss.

Although retrograde amnesia is not subject to temporal factors, several studies have shown the participation of an important temporal gradient in this type of alterations.

Specifically, in most cases of retrograde amnesia a coating of the memories is observed characterized by a greater resistance of the oldest memories.

This characteristic of retrograde amnesia is called Ribot's law and makes the majority of individuals with the disorder able to remember especially important events and information such as their name, their date of birth, the names of their relatives, etc.

Brain areas involved

The inability to access events that have occurred in the past characteristic of retrograde amnesia responds to the alteration of the functioning of different brain regions.

Specifically, research that has focused on delimiting the development of this alteration postulates three brain areas that seem to play a major role in retrograde amnesia: the hippocampus, the basal ganglia and the diencephalon.

Hippocampus

Hippocampus

Both the hippocampus and the surrounding brain regions (the medial temporal lobes) appear to be associated with the development of retrograde amnesia.

The hippocampus acts as the gateway for new information to the brain, which resides in this region before being stored in permanent memory.

In this way, injury to the hippocampus can cause the information stored in this brain structure to be unable to be transmitted to other regions and thus cause the absence of memory.

Basal ganglia

The basal ganglia are not brain structures that are directly related to the acquisition, storage and retrieval of information.

However, these brain structures perform the important function of producing acetylcholine, a neurotransmitter in the brain.

This substance seems to play an especially important role in memory processes and projects into the hippocampus and other regions of the cortex. For this reason, damage to the basal ganglia can cause an alteration in the production of acetylcholine and cause retrograde amnesia.

Diencephalon

Diencephalon

Finally, the diencephalon is one of the deepest and subcortical regions of the brain. This region does not carry out mnesic activities, however multiple studies have linked it to retrograde amnesia.

The association between diencephalon and amnesia lies mainly in the study of Korsakoff syndrome. This pathology deeply damages the diencephalon and presents one of its most prevalent symptoms, retrograde amnesia.

For this reason, although the mechanisms through which the diencephalon can affect memory are unknown, many authors postulate that this brain region could be important in the development of retrograde amnesia.

Causes

Retrograde amnesia is not a disease that is subject to a single cause. In fact, it is currently interpreted as a symptom that can appear in various diseases and specific situations.

Regardless of the cause of the amnesia, the alteration is characterized by the production of some type of damage in the previously described brain regions.

In this sense, several diseases and circumstances have been detected that seem to cause brain alterations and cause the experience of retrograde amnesia in the person.

The main ones seem to be: aging, head injuries, nutritional deficits and electroconvulsive therapy.

Aging

At present, it has been shown how aging produces a progressive deterioration of brain function. In this sense, retrograde amnesia can appear occasionally in advanced ages due to the deterioration of the brain regions involved with memory processes.

Head injuries

Head injuries usually present with the condition known as post-traumatic amnesia. In these cases, the blow to the head can damage brain regions and cause retrograde amnesia.

Nutritional deficits

The relationship between nutritional deficits and retrograde amnesia lies in Korsakoff's Syndrome, a pathology that is caused by vitamin B1 deficiencies, usually due to excessive alcohol consumption (alcoholism).

Electroconvulsive therapy

Finally, electroconvulsive therapy usually affects the patient's mnesic functioning and may, in some cases, lead to episodes of retrograde amnesia.

References

1. Evans, JJ, Breen, EK, Antoun, N., & Hodges, JR (1996). Focal retrograde amnesia for autobiographical events following cerebral vasculitis: A connectionist account, Neurocase, 2 (1), 1-11.
2. Nadel, L., & Moscovitch, M. (1997). Memory consolidation, retrograde amnesia and the hippocampal complex, Current Opinion in Neurobiology, 7 (2), 217-227.
3. Prigatano, G. (1987). Psychiatric aspects of head injury: Problem areas and suggested guidelines for research. Neurobehavioral Recovery from Head Injury, 217-218. New York: Oxford University Press.
4. Wixted, JT (2004). The psychology and neuroscience of forgetting, Annual Review of Psychology, 55, 235-269.
5. Wiggins, EC, & Brandt, J. (1988). The detection of simulated amnesia, Law and Human Behavior, 12 (1), 57-78.