Anterograde amnesia is the inability to retain new information following the trauma or event that causes amnesia, while memories made before the onset remain intact. Anterograde amnesia involves both episodic and semantic memory — the patient forgets both personally experienced memories and newly learned facts and concepts. While there are many theories, experts are still unsure of the specific way that anterograde amnesia interferes with memory.
Faulty Encoding
Some theories focus on faulty encoding as the cause of anterograde amnesia. They propose a problem with the initial presentation of information, which renders the person unable to process it into a more meaningful memory. Studies show that giving instructions or attempting to help a person with amnesia create connections does slightly improve retention. However, this improvement is also seen in control groups, so it is unlikely this theory is the only cause of anterograde amnesia.
Faulty Consolidation
Another theory for anterograde amnesia focuses on faulty consolidation. This means that the problem occurs after the presentation of the initial information when the brain is consolidating and transferring it from primary to secondary memory. Some questions surround this theory as it alone does not explain why the amnesia would last for an extended period unless there were also a problem with memory storage.
Faulty Storage
Faulty encoding or storage builds on the idea of faulty consolidation and focuses on contextual information. Generally, people with anterograde amnesia have a more difficult time with contextual memory or building associations that help with recall; however, this is not always the case. This theory has evolved to focus on the concept that people experiencing anterograde amnesia have trouble creating complex associations between information.
Accelerated Forgetting
Another possible cause of anterograde amnesia is accelerated forgetting. This theory proposes that the problem is not with learning the information, but retaining it. Some studies show that people with anterograde amnesia forget new learning in only a few minutes, whereas they recognize previously learned information at the same rate as people without amnesia.
Faulty Retrieval
There are two theories about anterograde amnesia and faulty retrieval. One is that retrieval is completely independent of acquisition, and the problem lies in the inability to recall. The other is that retrieval relies heavily on the initial memory encoding and that the deficits are a result of the initial impairment.
Retroactive Interference
A popular theory for anterograde amnesia is retroactve interference, an idea dating back to 1900. Retroactive interference is when information presented post-learning interferes with the recall of the learned material. Studies show that some people with anterograde amnesia retain new information much longer than expected, but introducing more new information interferes with this retention.
Causes
Regardless of how memory works in anterograde amnesia, experts do know that some conditions cause it. These include brain inflammation, poor brain oxygenation, alcohol abuse, brain tumors, seizures, and sedatives. Anterograde amnesia can also occur with head injuries. In mild injuries, it usually resolves with recovery, but it can be permanent in severe cases.
Diagnosis
To diagnose anterograde amnesia, the doctor performs a physical exam and takes a detailed medical history. They will spend a lot of time trying to understand the memory loss, to render an appropriate diagnosis. Other forms of memory loss, including dementia and Alzheimer’s disease, must be ruled out, and the doctor may order lab work or scans to rule out a brain tumor.
Cognitive Testing
The doctor will also perform cognitive tests to evaluate the patient’s judgment, thinking, and memory. The doctor may ask the person to repeat a list of words, name the current president, or recall personal information or past events. They will also perform a neurological exam that includes checking reflexes, balance, and other functions of the brain and nervous system.
Treatment
There is no cure or medication for anterograde amnesia, so treatment focuses on compensating for the memory problem and treating the underlying cause. Memory training, technological assistance, and low-tech memory aids, like calendars, photographs, and notebooks, are also helpful. While research is ongoing, memory and the brain are very complex, and it is unlikely that there is a single medication to treat anterograde amnesia.