What is anterograde amnesia and what are its symptoms?

We explain the causes and disorders that can cause this memory problem.

When we talk about someone suffering from amnesia, we automatically think of a person who does not remember his or her past. There is another type of amnesia, anterograde amnesia, which is the inability to form new memories..

This memory problem usually goes hand in hand with retrograde amnesia, that of past episodes, but it is not always linked. It is, therefore, an independent form of amnesia with its own causes and altered mechanisms.

Causes of anterograde amnesia

The causes of brain lesions can be very diverseThe causes of anterograde amnesia can be very diverse: cranioencephalic trauma, hypoxia, herpetic encephalitis or vascular problems. The lesion that causes the purest anterograde amnesia is the lesion of the anterior thalamus, usually of vascular origin.

In addition, it is possible to lose pyramidal cells in the bilateral hippocampus due to lack of oxygen or a blow to the skull, causing an amnesia that can either be pure, or it can occur in conjunction with other types of amnesia.

What is the problem in this type of amnesia?

Roughly speaking, patients with anterograde amnesia cannot learn new information. They are unable to retain in the long term a name, a new face, or learn some kind of game they did not know before.

They have no perceptual problems, and have a good working memory. These patients can remember new information and work with it for a short period of time, but are unable to retain it and work with it for a long time. they are unable to retain and recall it after a few hours.. It is as if the new information, once it is no longer present, vanishes.

We know that in order to store information in memory, a process of encoding and storage must occur. Science, curious by nature, wonders exactly where in this process individuals with anterograde amnesia fail. Here are the most commonly used hypotheses.

1. Coding problems

There are hypotheses that support that it is a coding problem. The brain, although it receives sensory stimuli, has difficulty giving them meaning and extracting which are the most important features.

For example, patients with Korsakoff's syndrome have problems learning apple-cheese word pairs. Normally, this learning is facilitated because the two share a characteristic, but Korsakoffs fail to establish this relationship. However, this explanation is weak and does not seem to be the most fundamental.

2. Problems of consolidation

Another hypothesis is that the Biological processes responsible for transporting encoded information and storing it are impaired.. Thus, although the subject can process the information and work with it in the moment, he is unable to store it for later.

For example, a group of American soccer players were taken and, 30 seconds after suffering a concussion, they were asked what had happened. The players were able to explain the order of events well, but as time went on they were able to recall fewer and fewer events, showing that the memory had not been consolidated.

This theory does not provide an answer, however, to why the loss of these memories due to non-consolidation is gradual.

3. Problems with contextual information

From this hypothesis people with anterograde amnesia are said to lose the ability to store contextual information.. Although they can remember specific words, they are not able to relate them to anything. Thus, when asked to repeat the words they have heard before, because they do not relate these words to any previous situation, they are unable to retrieve them.

This hypothesis presents problems, as the deficit in context encoding is closely related to temporal lobe damage, and those patients who do not have damage to the temporal lobe may have anterograde amnesia without a specific contextual deficit.

4. Accelerated forgetting

The fourth possibility is that the processing and storage of memories is intact, the problem is that new information is forgotten very quickly.. However, it is a hypothesis that has contradictory scientific support that has not been replicated.

5. Retrieval problems

This understanding of anterograde amnesia is subdivided into two hypotheses. The "pure" retrieval dysfunction hypothesis states that there will be difficulties in accessing learned information regardless of how it was learned. learned regardless of how it was learned. The other hypothesis postulates that, since retrieval of information is highly dependent on how it was learned, the amnesic has problems accessing the memory because of an initial problem in encoding.

In summary, the different theories point to a problem in the acquisition and consolidation of information, with a more subtle impairment of the retrieval processes. The exact explanation as to why this acquisition problem occurs remains open. One of the possible explanations may be that the amnesic patient's brain is unable to relate different types of information, such as contextual information.