The term retrograde amnesia refers to loss of memories of events that occurred before the incident that triggered the retrograde amnesia.
Most often retrograde amnesia affects memories close to the incident and only rarely it affects distant memories. Also retrograde amnesia is usually accompanied by anterograde amnesia. Cases of pure retrograde amnesia are really rare.
The retrograde amnesia is associated with damage to 3 important areas of the brain: diencephalon, temporal lobes and hippocampus.
The hippocampus is known for his role in episodic memory consolidation. It usually transfers memories from short-term memory to long-term memory.
The temporal lobe has a very important role in processing the factual and semantic memory. It also helps the hippocampus consolidate long-term memory.
The role of the diencephalon is not yet fully understood.
There are two important types of retrograde amnesia: pure retrograde amnesia and temporally graded.
The cases of pure retrograde amnesia re very rare and in this case people will forget even who they are and other personal information. Most often retrograde amnesia occurs along with anterograde amnesia.
Temporally retrograde amnesia is the most common form of retrograde amnesia. Most often, after the onset of retrograde amnesia the recovery begins. But retrograde amnesia is not always recovering it might also progress as it is an unstable condition and the case of stable retrograde amnesia are really rare.
The mechanism of retrograde amnesia is not fully understood yet. The condition is usually associated with Korsakoff’s syndrome, head injuries and anterograde amnesia.
It seems the severity of it is related to the damaged are of the brain. For example if damage is limited to the area CA1 of the hippocampus, the retrograde amnesia is limited at about 1 to 2 years. More extensive damage to the hippocampus might lead to retrograde amnesia that is limited at about 15 to 25 years.
A recent study showed that large lesions in the medial temporal lobe lead to a very extended retrograde amnesia that might cover 40 to 50 years.
Traumatic brain injury or TBI is another cause of retrograde amnesia. It usually occurs when an external force causes damage to the brain like for example a blow to the head. Traumatic brain injury might be involved in retrograde amnesia though it is not always involved.
Anyway, there were specific cases when severe blows to the head caused retrograde amnesia. In most of these cases the brain damage did not cause anterograde amnesia which means specific areas of the brain responsible with retrograde amnesia might be independent from areas responsible with anterograde amnesia.
But sometimes physical, anatomical damage that affects the brain directly might not be necessary. Sometimes retrograde amnesia might be triggered by traumatic situations which individuals avoid consciously or unconsciously.
There are studies of specific cases that support the possibility that traumatic events might trigger retrograde amnesia. Also stress variations might trigger retrograde amnesia and might as well produce new memories.
In case of accidents that involve head injury or memory loss people should call a doctor immediately.
Retrograde amnesia was found very common in people who suffer from Korsakoff’s syndrome which is associated with a poor diet and alcohol abuse. The diet of people affected by Korsakoff’s syndrome consists most often in large amounts of alcohol.
Other possible causes of retrograde amnesia include infections that might damage the brain or surgery that involves removal of certain parts of the brain.
To diagnose a person with retrograde amnesia there are a few specific tests. Most often autobiographical knowledge is tested using Autobiographical Memory Interview.
Also abnormalities in the brain can be detected and measured using CT (computed tomography) scan, MRI (magnetic resonance imaging) and EEG (electroencephalography).
The legal system is currently pushing for standard tests as many criminal report having retrograde amnesia to avoid punishment.
Most often recovery from retrograde amnesia is spontaneous.