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, anterograde 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, an independent form of amnesia with its own causes and altered mechanisms.
The causes of brain injuries can be very diverse: head 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 may be pure, or may occur together 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 incapable of long-term retention of a name, a new face, or learning some type of game that they did not 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 They are unable to retain it and remember it after a few hours. It is as if new information, once it is no longer present, vanishes.
We know that to store information in memory, it is necessary for an encoding and storage process to occur. Science, curious by nature, asks exactly where in this process individuals with anterograde amnesia fail. Below are the most used hypotheses.
1. Coding problems
There are hypotheses that support that it is a coding problem. The brain, even if it receives sensory stimuli, has difficulty giving them meaning and extracting which are the most important characteristics.
For example, patients with Korsakoff syndrome have problems learning apple-cheese word pairs. Normally, this learning is facilitated because both things share a characteristic, but the Korsakoffs fail to establish this relationship. However, this explanation is weak and does not seem the most fundamental.
2. Consolidation problems
Another hypothesis suggests that the biological processes responsible for transporting encoded information and storing it are damaged. Thus, although the subject can process the information and work with it at the moment, he 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 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 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. For this reason, 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 that the deficit in context encoding is closely related to damage to the temporal lobe, and those patients who do not have damage to it may have anterograde amnesia without a specific contextual 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 anterograde amnesia is subdivided into two hypotheses. The hypothesis of “pure” dysfunction in recovery says that there will be difficulties in accessing information learned regardless of how it was learned. The other hypothesis postulates that, since the retrieval of information depends a lot on how it was learned, the amnesiac has problems accessing the memory due to 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 impact on retrieval processes. The exact explanation for why this acquisition problem occurs remains up in the air. 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.
