Generality
Anterograde amnesia is a disorder characterized by the inability to fix memories of events following severe brain damage .
This form of memory loss does not, therefore, affect the memories that were already part of the memory heritage (a phenomenon that occurs, instead, in retrograde amnesia), but affects the storage of new information.
The causes of anterograde amnesia are to be found in the brain. This condition can derive, in particular, from traumatic lesions, degenerative processes, metabolic disorders and various other problems affecting the hippocampus or some areas of the temporal lobe.
The diagnosis of anterograde amnesia is based on the anamnesis and is formulated following a neuroradiological examination (eg computerized tomography, magnetic resonance, etc.). Treatment depends on the cause and focuses on problem management. These interventions may include psychotherapy or other techniques that help improve the quality of life, sometimes in association with specific exercises, memory aids or dietary supplements. Some cases of anterograde amnesia are temporary, others are permanent. Therefore, the symptoms of the disorder can improve, remain the same or worsen over time.
What's this
Anterograde amnesia is the loss of the ability to "store" new memories, following the causal event or the onset of the disease. In practice, the patient is unable to memorize the information or events that follow one another from a certain moment on, while the memories before the brain damage remain unchanged.
The result is a partial or complete inability to recall the recent past, even if long-term memories, stored before the event that caused the amnesia, remain intact.
Individuals with anterograde amnesia can repeat, for example, a question several times or fail to recognize the people they met a few minutes before.
Retro-anterograde amnesia
The anterograde amnesia involves a selective defect of fixation and, sometimes, of re-evocation (in the latter case, we speak of retro-anterograde amnesia).
Causes
In the learning process, memory, understood as a method of preserving information, plays an essential role. It may happen that we do not remember some events of our life that happened a long time ago or yesterday, but when brain injuries occur memory loss can be more serious, defining a clinical picture of AMNESIA .
Anterograde amnesia is a selective memory deficiency that fundamentally depends on brain damage . Because of this event, the subject has serious difficulties in storing new information, while memories prior to the disease remain intact.
Brain damage at the base of anterograde amnesia leads to severe impairment of short-term memory (MBT) .
Generally speaking, mild brain injuries can lead to short-term memory loss and symptoms can improve as the brain heals. Moderate to severe brain damage can lead to permanent anterograde amnesia.
Anterograde amnesia can be drug-induced (some benzodiazepines are known to have powerful amnesic effects, just as alcohol intoxication produces a similar manifestation) or to be the consequence of a traumatic brain injury, in which damage to the hippocampus or medial temporal lobe. At other times, the disorder is the result of an acute event such as a concussion, a heart attack, oxygen deprivation or an epileptic seizure. Less commonly, it can also be caused by a shock or emotional disturbance.
What parts of the brain are involved?
The parts of the brain affected by the damage at the origin of the anterograde amnesia are generally the HIPPOCAMPO and some areas of the temporal lobe associated with it.
Why in the hippocampus? The hippocampus is a "passage" area, in which information is stored temporarily, until it is transmitted to the frontal lobe. The hippocampus is, therefore, a sort of archive for short memory (the one capable of keeping a few elements for a few seconds); if this does not behave as such, it will be difficult or impossible to store the memories.
Damage to the hippocampus and surrounding areas is often the result of cerebrovascular accidents (ischemia, hemorrhage, etc.), aneurysms, epilepsy, encephalitis, hypoxia or carbon monoxide poisoning. These lesions are also observed in the early stages of degenerative diseases, such as Alzheimer's.
Anterograde amnesia can present also as a result of a damage to the DIENCEFALO; currently, however, the basis of this phenomenon remains to be clarified.
An example of a pathology that manifests itself with anterograde amnesia and depends on damage to the diencephalic structures involved in memory is Korsakoff syndrome . This condition is determined by the nutritional deficiency of vitamin B1 (thiamine) and occurs in many cases of chronic alcohol abuse.
What pathological conditions cause anterograde amnesia?
Anterograde amnesia is often the consequence of:
- Cerebrovascular problems (like an aneurysm);
- Epilepsy ;
- Brain hypoxia (due to ischemia, stroke or other conditions that lead to a reduction in the supply of oxygen to the blood);
- Carbon monoxide intoxication .
The anterograde amnesia is also found in the initial phase of Alzheimer's disease .
Other conditions that can cause anterograde amnesia include:
- Lobectomy (neurosurgical intervention usually performed to treat severe, drug-resistant seizures);
- Infectious diseases (eg herpes simplex virus encephalitis);
- Brain hemorrhages;
- Korsakoff syndrome (vitamin B1 deficiency);
- Brain tumors;
- Drugs, such as benzodiazepines;
- Chronic alcohol abuse;
- Sports injuries or car accidents;
- Dementia;
- Neurodegenerative diseases;
- Electroconvulsive therapy (ECT).
Symptoms and Complications
The main symptom of anterograde amnesia is memory loss . This manifests itself, in particular, as the clear inability to remember and learn new information from the moment the problem arose.
However, the loss of memory does not compromise what has been stored in the past: those who suffer from anterograde amnesia can remember with clarity only the events prior to the triggering condition.
A curious aspect of anterograde amnesia is that some people who suffer from this type of amnesia can acquire new skills or habits, even learn new games or write in reverse.
How Anterograde Amnesia Occurs
The symptoms of anterograde amnesia depend on the cause from which it derives and mainly concern the processing of short-term memory .
In general, the person who suffers manifests:
- Memory loss;
- Inability to recognize people's faces or familiar places;
- Confusion, frustration and disorientation.
Usually, those who suffer from anterograde amnesia only lose their declarative memory (which coincides with the memory of facts accessible to awareness), but preserve the procedural or implicit memory (that is, the learning of skills and habits, of how things are done and of how objects are used).
More specifically, patients with anterograde amnesia often lose only the episodic part of their declarative memory (that part which refers to autobiographical information inserted in a temporal and / or spatial context) and not the semantic part (general knowledge, as a language, history, geography, etc.).
How to recognize it
Anterograde amnesia prevents learning new information from the onset of the morbid event onwards.
Anterograde amnesia is characterized by severe short-term memory dysfunction: after the slightest distraction, for example, a person can forget all the conversation he was having.
In the transitory forms and in the initial phase of the persistent forms, anterograde amnesia is responsible for a particular phenomenon: the patient manifests a state of anxiety that leads him to ask for explanations through the continuous repetition of the questions, due to the immediate forgetfulness of the answer obtained and the question asked.
How long does anterograde amnesia last?
Anterograde amnesia can be:
- Transient (as often happens after mild brain trauma);
- Stable (as occurs after a serious morbid event such as an encephalitis, a global ischemia or a cardiac arrest);
- Progressive (as occurs in dementia on a degenerative basis, such as Alzheimer's disease).
Over time, when there is damage to only one side of the medial temporal lobe, the neuroplasticity of the brain (ie its ability to re-map its neural connections when necessary) can often allow the patient suffering from anterograde amnesia the opportunity of a normal (or almost) functioning, for memorizing memories.
Diagnosis
The diagnosis of anterograde amnesia is based on clinical, psychiatric and neurological evaluation.
The investigations aimed at defining the condition include:
- Specific neurological tests: they are useful to better understand the nature of the amnesic experience;
- Magnetic resonance to assess the presence of possible structural causes;
- PET (positron emission tomography) : is a survey that highlights the metabolic alterations of the brain;
- Blood and urine tests to exclude intoxication, the use of psychotropic substances or treatable metabolic causes.
Therapy
Treatment of anterograde amnesia depends on the cause of the problem. Some patients recover their memories and the condition is resolved, especially if appropriate assistance measures are arranged. Other people, however, fail to return to normal and their daily routine is strongly influenced by the disorder.
The treatment of anterograde amnesia focuses on improving the quality of life of the patient.
Options include:
- Memory training;
- Food supplements based on vitamin B1, in case of deficiency;
- Occupational therapy;
- Psychotherapy;
- Technological assistance to facilitate mnemonic recovery.
At the moment, there are no medicines approved to treat anterograde amnesia, but the use of drug therapy can be indicated by the doctor to reduce anxiety-depressive symptoms, irritability and insomnia, hyperactivation and disorganization of thought. Among the most used medicines there are: antidepressants, anxiolytics, neuroleptics or antipsychotic drugs.
In less severe cases, patients are educated to use alternative memory systems to compensate for brain inability. For example, it may be helpful to note the activities to be performed daily on small boards or notebooks. Furthermore, it is possible to equip the bathroom and the kitchen with safety devices or eliminate what could cause domestic accidents.
