What is antegrade amnesia and what are its symptoms?
When we talk about someone suffering from amnesia, we automatically think of a person who does not remember his past. There is another type, antegrade amnesia, which consists of 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 a form of independent amnesia with its own causes and altered mechanisms.
Causes of antegrade amnesia
The causes of brain injuries can be very diverse : head trauma, hypoxia, herpes encephalitis or vascular problems. The injury that causes the most pure anterograde amnesia is the injury of the anterior thalamus, normally of vascular origin.
In addition, it is possible to lose pyramidal cells in the bilateral hippocampus due to a lack of oxygen or a blow to the skull, causing an amnesia that may either be pure or may occur in conjunction with other types of amnesia.
What’s the problem with this kind of amnesia?
Roughly speaking, patients with antegrade amnesia cannot learn new information. They are unable to retain a name, a new face, or learn some kind of game they didn’t know before.
They have no perception problems, and they 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 and remember it after a few hours . It is as if the new information, once it is no longer present, disappears.
We know that in order to save information in memory, a process of coding and storage must occur. Science, curious by nature, asks exactly at what point in this process individuals with antegrade amnesia fail. Below are the most commonly used hypotheses.
1. Coding problems
There are hypotheses that support that this is a coding problem. The brain, although it receives sensory stimuli, has difficulty giving them meaning and extracting what are the most important characteristics.
For example, patients with Korsakoff’s syndrome have trouble learning apple-cheese word pairs. Normally, this learning is facilitated because the two share one characteristic, but the Korsakoffs fail to establish this relationship. However, this explanation is weak and does not seem to be the most fundamental.
2. Consolidation problems
Another hypothesis states that the biological processes in charge of transporting the encoded information and storing it are damaged . Thus, although the subject can process the information and work with it in the moment, he is unable to save it for later.
For example, it took a group of football players who, 30 seconds after suffering a concussion, were asked what had happened. The players were able to explain the order of events well, but as time passed they were able to remember fewer and fewer events, showing that the memory had not been consolidated.
This theory does not answer, however, why the loss of these memories due to non-consolidation is gradual.
3. Problems with contextual information
From this hypothesis it is said that people with anterograde amnesia lose the function of saving contextual information . Although they can remember concrete words, they are not able to relate them to anything. Therefore, when they are asked to repeat the words they have heard before, as they do not relate these words to any previous situation, they are unable to retrieve them.
This hypothesis presents problems, such as that the deficit in context coding is closely related to temporal lobe damage, and those patients who do not have damage to the temporal lobe may have antegrade amnesia without a specific context deficit.
4. Accelerated forgetting
The fourth possibility says 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 able to be replicated.
5. Recovery problems
This way of understanding antegrade amnesia is subdivided into two hypotheses. The hypothesis of “pure” dysfunction in recovery says that there will be difficulties in accessing the information learned regardless of how it was learned. The other hypothesis postulates that, as the retrieval of information depends a lot on how it has been learned, the amnesiac has problems accessing the memory because of an initial problem in the coding.
In summary, the different theories point to a problem in the acquisition and consolidation of information, with a more subtle affectation of the recovery processes. The exact explanation as to why this acquisition problem occurs is still up in the air. One of the possible explanations may be that the brain of the amnesiac patient is unable to relate different types of information, such as contextual information.