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Amnesia

life science Maturity 11-13 Next article →

Amnesia is a significant deficit in memory caused by brain damage or various brain diseases. It can also occur temporarily due to the use of certain sedative or hypnotic drugs. This condition affects how a person stores and retrieves information from their past and present. The extent of the memory loss can range from being a partial deficit to a total loss. This variation depends heavily on the specific nature and scale of the damage to the brain.

Types of Retrograde Amnesia Flowchart
Types of Retrograde Amnesia Flowchart

Understanding amnesia helps scientists learn how the brain organizes different types of knowledge.

There are two primary types of amnesia: retrograde and anterograde. Retrograde amnesia is the inability to recall information that was acquired before a specific date. This date is often the time of a medical operation or an accident. The loss can span only a few months or reach back many decades. Anterograde amnesia is the inability to transfer new information from short-term storage into long-term storage. People with this condition struggle to remember things for any significant length of time. These two types can also occur at the same time in a single person.

Researchers recognize several other distinct forms of memory impairment. Transient global amnesia is a temporary loss of memory that arrives suddenly. Dissociative amnesia is linked to intense emotional stress and involves an inability to recall personal experiences. Childhood amnesia refers to the common loss of early life memories seen across individuals. Post-traumatic amnesia can follow a head injury and involves confusion regarding events near the time of the trauma. Each of these forms represents a different way the brain's memory systems can fail.

Memory functions are tied to specific biological structures within the brain. Case studies show that amnesia is frequently associated with damage to the medial temporal lobe. Specific areas of the hippocampus, such as the CA1 region, are also vital for memory. Damage to the CA1 pyramidal cells can prevent the hippocampus from making connections to the cortex. This often results in a failure to form new episodic memories. Additionally, damage to the diencephalon can cause amnesia. Recent studies also show a correlation between a deficiency of the RbAp48 protein and memory loss. In mice, lower levels of this protein are found in those with damaged memory.

Scientists categorize the causes of amnesia into three general groups. The first group is head trauma, which includes any injury or active action toward the brain. The second group includes traumatic events, which are subjective and depend on what a person finds distressing. For example, dissociative amnesia can occur after a person witnesses a fatal car accident. The third group is physical deficiencies, which are more passive issues. These include Alzheimer's disease, vitamin B12 deficiency, or neurological syndromes like anti-NMDA receptor encephalitis. Other specific causes include alcohol use, strokes, and even the use of fentanyl.

Memory is not a single system, but is divided into declarative and non-declarative types. Declarative memory includes semantic memory, which is facts, and episodic memory, which is related to personal events. A patient named LSJ experienced retrograde declarative memory loss from medial temporal lobe damage. However, she could still remember how to perform specific declarative skills like reading music or art techniques. In contrast, non-declarative memory involves skills and implicit learning. This includes procedural memory, which is the memory for how to perform tasks. Patients can often learn new procedural knowledge even if they cannot consciously recall the learning event.

Even with profound impairments, many intellectual and social skills remain intact. Individuals with amnesia often retain their linguistic abilities and social skills. They may also benefit from perceptual priming, which is a form of non-declarative memory. In priming, a person has no conscious recall of an event but still shows a response to it. This was seen in patients who performed well on word fragment completion tasks. While anterograde amnesia cannot be treated with drugs due to neuronal loss, support is vital. Educating patients on daily routines can help utilize their intact procedural memory to improve their quality of life.

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File:Types of Retrograde Amnesia Flowchart.svg
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