Amnesia

Amnesia
Is a disturbance of the brain that causes the person to forget a period of his or her life. Despite being a popular plot in movies and novels, amnesia is quite rare in real life. There are two basic causes of amnesia: organic, where the brain is actually damaged, and functional, where the causes are psychological. Amnesia can happen to anybody, at any age.

What types of amnesia arethere?

Anterograde amnesia

Retrograde amnesia

Post Traumatic Amnesia (PTA)

Transient global amnesia

Wernike-Korsakoff's psychosis

Hysterical (fugue) amnesia

Infantile/childhood amnesia

Anterograde Amnesia
Is a condition in which an individual is unable to form new memories? His old memories still exist and his short-term memory is still functional, but he is unable tocommit new information into his long-term memory. Anterograde amnesia is almost always the direct result of some form of brain injury or trauma, but the exact cause of it, as well as the precise mechanism of memory formation and storage, is not fully understood. Conversely, retrograde amnesia is a condition in which an individual loses memories that are formed prior to some incident that causes braindamage.
There are a few different parts of the brain that have been linked to anterograde amnesia. A great deal of new information must pass through the hippocampus before it is committed to permanent memory; as such, damage to the hippocampus can prevent memory formation. The basal forebrain contains structures that produce chemicals important to learning, making it essential to memory formationas well. Other less prominent parts of the brain have also been linked to anterograde amnesia, though the connection between the structures and memory formation is often poorly understood.
The severity of anterograde amnesia can vary from case to case, but it always involves severe forgetfulness. Sometimes amnesia is chemically induced for research purposes; in these cases it is temporary. Often,anterograde amnesia caused by brain damage is permanent. Over time, memory loss can get better or worse; there is no set rule describing the progression of learning impairment.
Not all forms of learning are completely impossible for individuals with anterograde amnesia. While they are often incapable of recalling any facts concerning anything that occurred since they suffered brain damage,individuals suffering from amnesia may still find it possible to learn skills. Studies have shown that while an individual who is not able to form new memories will have no recollection of learning a new skill; he will often be able to perform a new skill without being taught again. This is because his declarative memory is impaired while his procedural memory continues to function.

AnterogradeAmnesia

Is a selective memory deficit, resulting from brain injury, in which the individual is severely impaired in learning new information. Memories for events that occurred before the injury may be largely spared, but events that occurred since the injury may be lost. In practice, this means that an individual with amnesia may have good memory for childhood and for the years before the injury,but may remember little or nothing from the years since. Short-term memory is generally spared, which means that the individual may be able to carry on a conversation; but as soon as he is distracted, the memory of the conversation fades.

Anterograde amnesia can occur following damage to at least three distinct brain areas. The first, and most well-studied, is the hippocampus and associatedareas in the medial temporal lobes of the brain. The hippocampus seems to act as a "gateway" through which new fact information must pass before being permanently stored in memory. If it is damaged, no new information can enter memory - although older information which has already passed through the gateway may be safe. Damage to the hippocampus (and medial temporal lobes) can occur following...