An Overview of Anterograde Amnesia

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Anterograde amnesia is a condition in which a person is unable to create new memories after an amnesia-inducing event. Anterograde amnesia may involve either partial or total inability to remember events that have happened. At the same time, a person with this type of amnesia has intact long-term memories from before the incident.

Understanding the Different Types of Memory

Before we delve into more detail about anterograde amnesia, it will be helpful to learn a bit about the different types of memory that can be affected by amnesia.

First, we can divide memory into declarative or non-declarative and define each type to better understand the differences:

Declarative

  • This type of memory refers to the recollection of facts (whether as part of a specific event or just as unrelated information).


Non-Declarative

  • This type of memory is also known as procedural memory and refers to remembering how to do something such as riding a bike or making a phone call.

Declarative memory can be further divided into episodic and semantic memory, which refers to whether the memory involves connections to times or places or simple facts that can be recalled but not linked to any specific episode of time.

  • Episodic memory: Episodic memory refers to autobiographical information that includes temporal or spatial context. For example, you might remember what happened on a particular vacation.
  • Semantic memory: This type of memory refers to factual information without any associations to events that happened in your past. For example, you might remember that you own a bike, but don't remember where you bought it or where you have ridden it.

Understanding Anterograde Amnesia

A person with anterograde amnesia might remember how to make a phone call but they don't remember what they did earlier this morning. This is because declarative and non-declarative memories are thought to be stored in different areas of the brain. What's more, these individuals will often have lost the episodic part of declarative memory but not the semantic part.

Anterograde amnesia differs from retrograde amnesia in the timing of when memories are lost. People who have retrograde amnesia cannot remember things that happened before the event that caused their amnesia.

On the other hand, people with anterograde amnesia can often remember everything up until that event—but can't retain memories of things happening after that date. It is also possible for a single person to have both of these types of amnesia: this is referred to as severe global amnesia.

In essence, anterograde amnesia is thought to involve the failure to encode (or possibly retrieve) new memories. There are also different levels of severity of anterograde amnesia. Some people might forget a recent meal or a new phone number, while others might forget what they were doing 30 seconds ago. Task difficulty can also influence memory, with more complex tasks being more difficult to remember than simpler tasks that may require less brainpower.

Brain Areas Involved in Memory

What brain areas are involved in anterograde amnesia? There are several that we can consider. Research tells us it's likely that the hippocampus and nearby subcortical regions are implicated. The medial temporal lobe (MTL), basal forebrain, and fornix have all been considered as potential parts of the brain that may play a role.

The MTL system comprises the hippocampal, perirhinal, entorhinal, and parahippocampal areas and is important for factual recall (declarative memory). On the other hand, the MTL is not involved in non-declarative memory.

We also know that impairments tend to affect all modalities (sound, touch, sight, taste, smell).

Causes of Anterograde Amnesia

There are multiple potential causes of anterograde amnesia, which are all involved with some sort of trauma or stress to the brain.

Drug use: Short-term anterograde amnesia may result from the use of certain drugs.

Benzodiazepines: This type of medication has been linked to anterograde amnesia, along with the use of non-benzodiazepine sedatives such as zolpidem (Ambien).

Traumatic brain injury: Damage to the hippocampus or surrounding area has been linked to the presence of anterograde amnesia.

Brain inflammation: Inflammation of the brain such as encephalitis has been linked to signs of anterograde amnesia.

Brain surgery: Patients who had parts of the brain removed, such as the MTL, have shown to have impairments related to anterograde amnesia.

Stroke: Stroke has been linked to memory impairment and cognitive deficits due to changes in brain structures.

Alcohol blackout: A person who consumes a large amount of alcohol in a short period of time may experience a loss of memory for the time period that they were drinking. However, after the episode, their memory functioning would return to normal.

Chronic alcoholism: On the other hand, chronic alcoholism can lead to thiamine (B1) deficiency, leading to Korsakoff's syndrome, which causes significant problems in anterograde episodic memory.

Concussion/sports injury: Concussion and sports injury to the head have been linked to anterograde amnesia.

Treatment of Anterograde Amnesia

While there is no cure for anterograde amnesia, some recovery and rehabilitation may be possible even with permanent damage. At the same time, there is no medication treatment for amnesia. Instead, the following compensatory strategies are recommended:

  • Reminder beepers
  • Journals/notes/diaries
  • Family support
  • Occupational therapy

Case Studies With Anterograde Amnesia

In the most famous case study of a person with anterograde amnesia, the patient known as H.M. was shown to be able to learn how to complete a maze, even though he had no memory of having completed the maze before. H.M. was suffering from anterograde amnesia due to surgery conducted to cure his epilepsy.

Another famous case study of anterograde amnesia is that of Clive Wearing who contracted herpes simplex virus and related complications to his brain. After this event, Wearing developed significant retrograde and anterograde amnesia. However, he retained his ability to play piano and conduct a choir.

Anterograde Amnesia in Film

There are several well-known movie characters with anterograde amnesia as the short-term memory deficit can make for some interesting, funny, and suspenseful scenes. Unfortunately, as entertaining as these movies may be, the true nature of the impairment can be severely debilitating.

Take the character Leonard Shelby in the movie Memento, for instance. In Memento, the main character kept notes on himself to keep on track as he tried to solve a crime despite his anterograde amnesia. It's been said that Memento is the closest representation to what actual anterograde amnesia is like, particularly given the way in which the movie is filmed to reflect the character's memory impairments.

Diagnosis of Anterograde Amnesia

The work-up of anterograde amnesia may involve using brain scan technology such as magnetic resonance imaging (MRI) and CT scan. In addition, the doctor will ask questions to understand the memory loss such as whether long-term or recent memory is affected, when the memory issue started, what the causal factor may have been, if there is any family history of similar problems, any substance use, history of seizures, and related problems such as confusion, language issues, or personality changes.

A Word From Verywell

If you or someone you know is living with anterograde amnesia, it may be hard to know how to cope or how to help your loved one. This type of impairment can affect daily functioning, particularly if it is severe. Having the support of family and friends is critical and should be part of any treatment plan if possible. If you are finding that you are struggling to cope with your condition, further treatment options with new strategies for managing your impairment may be in order.

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