Post-traumatic amnesia or post-traumatic amnesic syndrome often occurs in subjects who have suffered head injuries and can persist for years, seriously affecting the memory of events. Let’s see what its characteristics are.

Post-traumatic amnesia: definition

The term post-traumatic amnesia was first coined by the English neurologist Charles P. Symonds to refer to a general alteration of brain function after consciousness has been recovered . Current research defines post-traumatic amnesia as a persistent, stable and global memory impairment, due to an organic brain disorder, in the absence of other types of cognitive deficits.

In post-traumatic amnesia, there is difficulty in evoking and acquiring new information; the subject is unable to keep a continuous record of his or her daily activities. This syndrome often occurs in moderate and severe traumatic brain injury (TBI), along with permanent mnestic deficits.

These memory deficits are mainly due to focal lesions in the hippocampus (structure closely linked to memory and special location) and adjacent structures, as well as other diffuse brain damage.

Characteristics of this syndrome

Post-traumatic amnesia is the result of the sum of several factors such as loss of consciousness caused by the injury, retrograde amnesia ranging from a few minutes to years before the accident and anterograde amnesia ranging from a few hours to months after recovery of consciousness.

This mnestic syndrome is composed of several factors such as loss of consciousness from the injury or trauma, retrograde amnesia (inability to remember events that occurred before the injury), and sometimes anterograde amnesia. Parkin and Leng defined the following characteristics of post-traumatic amnesia :

  • There is no short-term memory deficit (assessed by tasks such as digit span).
  • The semantic memory, in charge of encoding, storing and retrieving learned information, is not affected.
  • Permanent inability to store new information after the injury (assessed by evocation and recognition tests)
  • In some patients, inability to retrieve information stored in long-term memory prior to the injury
  • Procedural memory (in charge of the memory of motor and executive skills) is not affected.
  • Motor skills are preserved and the subject is able to form new memories in the procedural memory.

What can cause this memory impairment?

Blows and traumas to the head and skull are the best known causes when referring to post-traumatic amnesia. However, there are other factors -some of them avoidable- to be taken into account in order to know what can cause such a syndrome.

1. Stroke

A stroke happens when blood flow to the brain stops and the brain can no longer receive oxygen and nutrients. Neurons can die, causing permanent functional and structural damage.

2. Encephalitis

Encephalitis or inflammation of the brain can result from a viral infection (for example, the herpes simplex virus) or as an autoimmune reaction to cancer.

3. Hypoxia or anoxia

Hypoxia, when there is a lack of oxygen, and anoxia, when there is a total absence of oxygen , may be causative factors in post-traumatic amnesia. This lack of oxygen may be due to a heart attack, respiratory distress, or carbon monoxide poisoning, for example.

4. Alcohol abuse

Long-term alcohol abuse can lead to thiamine (vitamin B1) deficiency. A severe deficiency of this vitamin can lead to brain damage and the development of Wernicke-Korsakoff syndrome , a brain disease that causes injury to the thalamus and hypothalamus, resulting in irreversible damage to cognitive functions such as memory.

5. Degenerative diseases, tumors and other pathologies

Degenerative brain diseases, tumours and other pathologies such as cancer can cause mnestic syndromes depending on the areas of the brain affected.

Symptoms

Post-traumatic amnesia is usually accompanied by severe temporal and spatial disorientation, attentional deficits (mainly in sustained and focused attention), retrograde and anterograde amnesia, confabulation, agitation and uninhibited behavior.

During the course of the syndrome, patients feel confused, disoriented and have great difficulty in processing the information coming from the environment . Depending on the intensity of the injury, patients will remember with greater or lesser difficulty the events surrounding the accident or minutes before.

With regard to language, subjects suffering from post-traumatic amnesia often present an incoherent discourse and their perception of the environment and new stimuli is distorted, which generates an exacerbation of confusion and fear.

It is also common for patients to be aggressive (physically or verbally) and restless. In addition, people with post-traumatic amnesia syndrome may have hallucinations .

Other mnestic deficits

In addition to post-traumatic amnesia, there are other types of mnestic syndromes in which different types of memory are affected in various brain areas. The following are the most common:

Temporary amnesia syndrome

In amnesias where the medial temporal lobe is affected , the patient usually presents an antegrade episodic and semantic amnesia (affecting both general and personal and autobiographical information) and a retrograde amnesia. However, short-term and procedural memory is preserved.

Diencephalic amnesic syndrome

In diencephalic amnesias patients present retrograde amnesia and antegrade amnesia (both semantic and episodic) which cannot always be explained by an inability to store information but may be partly related to a memory disorder, an element which distinguishes them from temporary amnesias.

On the other hand, in this syndrome there is also a deficit in metamemory (capacity to assess one’s own memory capacity)

3. Frontal amnesia syndrome

Amnesias for injury to the frontal cortex do not produce a global loss of memory , since this area of the brain is in charge of strategic processes of recovery, monitoring and verification of information. On the other hand, patients do see their capacity to search and select relevant information for each situation and context diminished.

4. Semantic dementia

This type of amnesia syndrome has a significant effect on declarative retrograde memory (responsible for storing memories and events in our lives that can be expressed explicitly). However, non-declarative memory, language grammar and other cognitive functions are preserved.

Bibliographic references:

  • Fernández-Ballesteros, R. (2005). Introduction to Psychological Evaluation I and II. Pirámide Publishing House. Madrid.
  • Kolb, B. & Wishaw, I.Q. (2006) Human Neuropsychology (5th Ed.). Editorial Médica Panaméricana: Buenos Aires.