What Is Anterograde Amnesia?

There are five major characteristics of the disease:

Anterograde amnesia

An antegrade amnesia is amnesia in which things happen after the event that caused the amnesia. This disease, unlike retrograde amnesia, is not about forgetting what happened before the memory loss event. To a large extent, because people don't thoroughly study the exact mechanism of memory, scientists can only point out which part of the brain is working, and antegrade amnesia is still a very mysterious disease.

Anterograde amnesia concept

There are five major characteristics of the disease:

First: anterograde amnesia affects long-term memory but does not affect working memory;

Second: the memory obtained from any channel, regardless of sight, hearing, kinesthetic,

Smell, taste or tactile information-all affected by anterograde amnesia.

Third: antegrade amnesia retains the general knowledge learned before the onset of amnesia

Memories, but memories of new facts and events are severely impaired;

Fourth: Some forgotters have retained their skilled operation;

Fifth: When people with amnesia do learn a skill, they show super specificity

Sexual memory.

Causes of antegrade amnesia

The disease is mainly caused by the following two reasons: or due to the induction of some drugs Strong amnesia effect), or because of traumatic brain injury to the hippocampus or surrounding cortex of the brain.

Amnesia also occurs in patients who have had their brains removed in order to prevent more serious diseases, which may include memory circuits such as the mesotemporal (MTL) memory system. In general, patients with epilepsy caused by MTL disorders will have their unilateral or bilateral brain tissue removed (a piece of related tissue in each hemisphere). In addition, patients with brain tumors often damage these tissues after surgery. Damage to some systems, including the hippocampus and surrounding cortex, can cause amnesia.

Heavy drinking is also one of the causes of anterograde amnesia. This is often due to a blood alcohol concentration of more than 0.25% and a hangover.

Features of anterograde amnesia

Patients with antegrade amnesia will experience varying degrees of amnesia. Some severe patients have anterograde and retrograde amnesia, sometimes called "whole brain amnesia."

Cases of drug-induced amnesia are often short-term and recoverable. In other cases, patients have suffered permanent damage since studies in the early 1970s, although some cases have a theoretical possibility of recovery in pathophysiology. Usually, patients still have some of the most basic learning abilities, and for some patients with severe antegrade amnesia, they only have memories before amnesia, and they can't remember anything after amnesia.

In most cases, patients with antegrade amnesia lose declarative memory, or factual memory, but leave non-declarative memory, which is often called procedural memory. For example, they remember and may learn how to do things such as making phone calls, cycling, etc., but they cannot remember what they ate yesterday at noon. In addition, the patient's ability to remember the episode of the event decreased. According to some reports, the disease impairs episodic memory more than semantic learning.

Antegrade amnesia pathophysiology

The pathophysiology of anterograde amnesia varies greatly depending on the location and degree of damage to the brain. The most typical associated regions are the midtemporal lobe, basal forebrain, and cerebral fornix. Except for the following details, the precise principle of memory is still a mystery from a micro perspective. Neuropsychology and scientists have not fully agreed that forgetting is due to missing coding based on the memory coding hypothesis, speeding up forgetting, or missing retrieval.

Anterograde amnesia (1) middle temporal lobe

The mesotemporal memory system (MTL system) includes the hippocampal structure (CA area, dentate gyrus, inferior complex), the outer nasal cortex, the inner nasal cortex, and the hippocampal cortex. They play an important role in the process of storing and declarative memory. They are linked to the neocortex in the process of building and maintaining long-term memory, although their known functions are independent of long-term memory. In contrast, non-declarative memory, while controlling skills and habits, is not part of the mesotemporal memory system. Most of the data points to the division of labor in the various parts of the system.

In animal experiments, researchers have found that monkeys with damaged hippocampus and surrounding cortical areas have more severe antegrade amnesia than monkeys with only damaged hippocampus. However, other studies on primates have shown that the area of tissue destruction is not necessarily related to the degree of amnesia. In addition, the data failed to explain the differences between episodic and semantic memory in the mesotemporal memory system.

It is said that patients with amnesia who have damaged the mesotemporal memory system cause damage to all sensory forms, including hearing, vision, smell, taste, touch, etc., thus confirming that the mesotemporal memory system is a processor of sensory forms, and then These thoughts are organized as memories. In addition, the system remembers how to perform relatively simple actions immediately (in about 10 seconds), but forgets more complex actions, even if it only takes a short time. This proves the difficulty of separating procedural memory from declarative memory; certain elements of declarative memory may be used to perform procedural activities.

In particular, the mesentemporal lobe memory system retains other perceptual abilities only in amnesiacs with damaged hippocampus, such as dealing with people, talking, making beds, and so on. Moreover, patients with pure antegrade amnesia (only for damage to the MTL system) retain memory before the amnesia-causing event. Therefore, MTL is not a storage place for all memories, and other brain regions also store memories. The key to MTL is the ability to learn and translate into memory.

Anterograde amnesia (2) other memory systems

A few cases indicate that patients who have damaged other parts of the brain will have antegrade amnesia. Easton and Parker found that damage to the primate's hippocampus and surrounding cortex did not cause severe amnesia. They claim that damage to the hippocampus and surrounding structures alone did not cause the symptoms described in amnesia or to the extent described. In addition, the data does not explain the segmentation of episodic and semantic memory in MTL memory systems. To demonstrate their conjecture, they used a primate model that disrupted the basal forebrain. They proposed that damage to neurons projecting from the basal forebrain into the MTL system can cause some lesions of antegrade amnesia. Their report also suggested that MRI scans of patients with severe antegrade amnesia showed damage to the hippocampus, amygdala, and peripheral cortical areas of the surrounding white matter.

Fornix cell death is another cause of anterograde amnesia. The fornix carries information on the structure of the hippocampus to the limbic system and the mesencephalic system. This type of patient does not show any separation syndrome, that is, there is no related structure of the isolated hippocampus of the brain (the patient's brain can communicate normally). However, patients have amnesia. An MRI examination gives the final accurate result. This particular amnesia syndrome is difficult to detect and it is often treated by physicians as acute mental disorders.

Anterograde amnesia (3) memory reorganization

When unilateral MTL is impaired, memory is distributed in a normal or normal-like manner. Neuroplasticity refers to the ability of the cortex to reorganize when necessary. Restructuring can occur in any of these situations, and at the same time, the patient will recover and have a stronger memory. In a case where a double temporal lobe resection was performed, part of the right brain MTL was removed because of epilepsy, and then the left brain was also removed because of a tumor. This case is unique in that the patient's bilateral MTL was removed at different times. The experimenter found that the patient recovered part of his learning ability when he removed unilaterally, but the situation worsened after bilateral resection. Not much research has been done on brain reorganization in patients with epilepsy, but imaging results are promising.

Famous cases of anterograde amnesia

The most famous case is probably a patient named Henry Gustav Morleyson (often referred to as HM) reported by Scoville and Milner in 1957. The main complaints of HM are chronic severe epilepsy and bilateral temporal lobe resection (both sides of the MTL are removed). As a result, both the HM bilateral hippocampal structure and the outer nasal cortex were damaged. HM is normal in intelligence, perception, and expression, but he cannot learn new words and new things. He was the first to have a fully documented case of antegrade amnesia and has volunteered to participate in the study until his death in 2008.

Another case is patient EP, who has severe amnesia. In a three-word simple sentence learning test, he performed well in 24 consecutive learning sessions over 12 weeks, but when asked if he was sure of the answer, he was not very sure. Researchers Bayley and Squire believe that his learning process is like a process that requires procedural memory assistance; EP cannot answer correctly when a word or sequence of a three-character sentence changes, because most of his answers originate from "habits." Bayley and Squire stated that EP learning may occur in the neocortex and that it does not require cognitive knowledge to occur. They speculated that when the scene is repeated, the information can be directly received by the neocortex (the information projected by the hippocampus). This case demonstrates the difficulty of separating procedural memory from descriptive memory and illustrates the complexity of antegrade amnesia from another perspective.

Three major controversies in anterograde amnesia

Anterograde amnesia (1) plot and semantic memory

From the above discussion, we can know that patients with antegrade amnesia can have various symptoms. Declarative memory can be further divided into episodic and semantic memory. Plot memory is an autobiographical memory with information about time and / or space, while semantic memory is a memory of facts without contexts such as language, history, and geography. In a case of a girl with anterograde amnesia at an early age, the patient had severe episodic memory impairment in CL while maintaining semantic memory.

Vicari et al. Cannot determine whether the episodic and semantic neural circuits overlap partially or completely, and the above example seems to show that the two systems are independent. The left and right structures of the hippocampus and the interbrain of the patient are separated. The main complaints of the patient's CL included plot and semantic amnesia. After a series of neuropsychological tests, Vicari confirmed that CL performed well in visual naming tests and sentence comprehension tests, and that there was no problem with visual spatial abilities and "common sense of the world". They also found that patients' words and common sense accumulation increased after 18 months. But CL's episodic memory is far less than expected: she can't remember daily events, such as her vacation place name, places she visited, and similar information. However, similar studies, including this one, are subjective in distinguishing between plot and semantic memory, which has caused a lot of controversy.

Anterograde amnesia (2) distinction between familiarity and memory

We know that the issue of familiarity in performing space missions requires the participation of the right hippocampus, while the left hippocampus is involved in the familiarity of language tasks. Some researchers believe that the hippocampus is important for memory retrieval, while familiar basic memory is maintained by adjacent cortical regions. Some memories are determined by matching existing memories (pre-morbidity memories) with actual situations. According to Gilboa et al., Patients with locally damaged hippocampus can perform well on familiarity-based tests.

Poreh published a study of AD in a patient who injured the fornix. The patient's symptoms were extremely rare, his hippocampus was ineffective, and the adjacent cortical area was intact. If the patient is tested for what he is familiar with, the patient performs well. However, AD's episodic memory is severely impaired, but semantic knowledge can be learned. Other studies have shown that animals that suffer similar damage can recognize things that they are familiar with, but that they don't recognize something that unexpectedly appears.

Anterograde amnesia (3) island of memory

Patients with antegrade amnesia have difficulty recalling new information and new personal experiences, but the latter lacks unified data. Medveds and Hirst use many patient lists to record the existence of memory islands. The island of memory is a combination of episodic and semantic memory. Researchers have recorded many statements in patients with a lot of details similar to pre-injury memories. The performance of memory islands is related to the function of adjacent cortical regions and neocortex. In addition, researchers speculate that the amygdala plays a role in declarative memory.

Antegrade amnesia

* "Memory pieces"

* "First Love 50 Times"

* "Clean Slate"

* Fuddy Meers

* "Finding Nemo"

* The Lookout

* Ef-a fairy tale of the two.

* "unknown death"