What is anterograde amnesia and what symptoms does it present?
When we talk about someone suffering from amnesia, we automatically think of a person who does not remember their 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 anterograde amnesia
The causes that cause brain injuries can be very diverse : traumatic brain injuries, hypoxia, herpetic encephalitis or vascular problems. The lesion that causes 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 may be pure, or may occur in conjunction with other types of amnesia.
What is the problem in this type of amnesia?
Broadly speaking, patients with antegrade amnesia can not learn new information. They are unable to retain a long-term name, a new face, or learn some kind of game they did not know before.
They do not have perception problems, and they have a good working memory. These patients can remember new information and work with it for a short time, but are unable to retain it and remember it after a few hours . It is as if the new information, once it is no longer present, vanishes.
We know that to store information in memory, it is necessary that a coding and storage process occurs. Science, curious by nature, wonders exactly at what point in this process fail individuals with antegrade amnesia. Below the most used hypotheses.
1. Coding problems
There are hypotheses that support that it is a coding problem. The brain, although it receives the sensory stimuli, has difficulty giving them meaning and extracting which are the most important characteristics.
For example, patients with Korsakoff syndrome have trouble learning apple-cheese word pairs. Normally, this learning is facilitated because both things share a characteristic, but the Korsakoff fail to establish this relationship. However, this explanation is weak and does not seem the most fundamental.
2. Consolidation problems
Another hypothesis states that the biological processes responsible for transporting the encoded information and storing it are damaged . Thus, although the subject can process the information and work with it at the time, it is unable to save it for later.
For example, a group of American football players were taken who, 30 seconds after suffering a concussion, were asked what had happened. The players were able to explain the order of the events well, but as time passed they were able to remember 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 antegrade 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, by not relating these words to any previous situation, they are unable to recover them.
This hypothesis presents problems, such as the deficit in coding of the context is closely related to damage in the temporal lobe, and those patients who do not have it damaged may have anterograde amnesia without a specific contextual deficit.
4. Forgotten forgetfulness
The fourth possibility says that the processing and storage of memories is intact, the problem is that the new information is forgotten very quickly . However, it is a hypothesis that has contradictory scientific support that has not been replicated.
5. Recovery problems
This way of understanding anterograde amnesia is subdivided into two hypotheses. The hypothesis of "pure" dysfunction in recovery says that there will be difficulties in accessing information learned independently of how it was learned. The other hypothesis postulates that, as the information retrieval depends a lot on how it was learned, the amnesiac has problems accessing the memory due to 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 impact on the recovery processes. The exact explanation of why this acquisition problem occurs is in the air. One of the possible explanations may be that the amnestic patient's brain is unable to relate different types of information, such as contextual.