Biogenic and psychogenic forgetting

Biogenic and psychogenic forgetting

Alzheimer’s disease

n  Alzheimer’s is the most common cause of dementia in adult life and is associated with the selective damage of brain regions and neural circuits critical for memory and cognition

n  The pathogenesis of this disease is complex, and involves many molecular, cellular, and physiological pathologies

n  The neurons in the neocortex, hippocampus, amygdala, and the basal forebrain cholinergic system are the most affected brain regions

Alzheimer’s disease is an irreversible, progressive brain disease that slowly destroys memory and thinking skills and, eventually even the ability to carry out the simplest tasks of daily living. In most people with Alzheimer’s, symptoms first appear after age 65. Alzheimer’s disease is the most common cause of dementia among older people. Symptoms include having difficulty remembering things, making decisions and performing everyday activities. These changes can affect the way a person feels and acts.

The disease is named after Dr. Alois Alzheimer. In 1906, Dr. Alzheimer noticed changes in the brain tissue of a woman who had died of an unusual mental illness. Her symptoms included memory loss, language problems, and unpredictable behavior. After she died, he examined her brain and found many abnormal clumps (now called amyloid plaques) and tangled bundles of fibers (now called neurofibrillary tangles).

Plaques and tangles in the brain are two of the main features of Alzheimer’s disease. The third is the loss of connections between nerve cells (neurons) in the brain.

Although treatment can help manage symptoms in some people, currently there is no cure for this devastating disease.

Amnesia is a deficit in memory caused by brain damage, disease, or psychological trauma. Amnesia can also be caused temporarily by the use of various sedatives and hypnotic drugs. Essentially, amnesia is loss of memory. The memory can be either wholly or partially lost due to the extent of damage that was caused. There are two main types of amnesia: retrograde amnesia and anterograde amnesia. Retrograde amnesia is the inability to retrieve information that was acquired before a particular date, usually the date of an accident or operation. In some cases the memory loss can extend back decades, while in others the person may lose only a few months of memory. Anterograde amnesia is the inability to transfer new information from the short-term store into the long-term store. People with this type of amnesia cannot remember things for long periods of time. These two types are not mutually exclusive. Both can occur within a patient at one time.

French psychologist Theodule-Armand Ribot was among the first scientists to study amnesia. He proposed Ribot's Law which states that there is a time gradient in retrograde amnesia. The law follows a logical progression of memory-loss due to disease. First, a patient loses the recent memories, then personal memories, and finally intellectual memories. He implied that the most recent memories were lost first.

Retrograde amnesia refers to inability to recall memories before onset of amnesia. One may be able to encode new memories after the incident. Retrograde is usually caused by head trauma or brain damage to parts of the brain besides the hippocampus. The hippocampus is responsible for encoding new memory. Episodic memory is more likely to be affected than semantic memory. The damage is usually caused by head trauma, cerebrovascular accident, stroke, tumor, hypoxia, encephalitis, or chronic alcoholism. People suffering from retrograde amnesia are more likely to remember general knowledge rather than specifics. 

Anterograde amnesia refers to the inability to create new memories due to brain damage, while long-term memories from before the event remain intact. The brain damage can be caused by the effects of long-term alcoholism, severe malnutrition, stroke, head trauma, surgery, Wernicke-Korsakoff Syndrome, cerebrovascular events, anoxia or other trauma. The two brain regions related with this condition are medial temporal lobe and medial diencephalon. Anterograde amnesia can't be treated with pharmacological methods due to neuronal loss. However, treatment exists in educating patients to define their daily routines and after several steps they begin to benefit from their procedural memory. Likewise, social and emotional support is critical to improving quality of life for anterograde amnesia sufferers.

·         Childhood amnesia (also known as infantile amnesia) is the common inability to remember events from one's own childhood. Sigmund Freud notoriously attributed this to sexual repression, while modern scientific approaches generally attribute it to aspects of brain development or developmental psychology, including language development, which may be why people don't easily remember pre-language events. Researchers have found that implicit memories cannot be recalled or described. Remembering how to play the piano is a common example of implicit memory, as is walking, speaking and other everyday activities that would be difficult to focus on if they had to be relearned every time one got up in the morning. Explicit memories, on the other hand, can be recalled and described in words. Remembering the first day that you met your piano teacher is an example of explicit memories.

·         Korsakoff's syndrome can result from long-term alcoholism or malnutrition. It is caused by brain damage due to a vitamin B₁ deficiency and will be progressive if alcohol intake and nutrition pattern are not modified. Other neurological problems are likely to be present in combination with this type of Amnesia. Korsakoff's syndrome is also known to be connected with confabulation. It should be noted that the person's short-term memory may appear to be normal, but the person may have a difficult time attempting to recall a past story, or with unrelated words, as well as complicated patterns.

·         Post-traumatic amnesia is generally due to a head injury (example: a fall, a knock on the head). Traumatic amnesia is often transient, but may be permanent or either anterograde, retrograde, or mixed type. The extent of the period covered by the amnesia is related to the degree of injury and may give an indication of the prognosis for recovery of other functions. Mild trauma, such as a car accident that results in no more than mild whiplash, might cause the occupant of a car to have no memory of the moments just before the accident due to a brief interruption in the short/long-term memory transfer mechanism. The sufferer may also lose knowledge of who people are. Having longer periods of amnesia or consciousness after an injury may be an indication that recovery from remaining concussion symptoms will take much longer.