When a patient is diagnosed with retrograde amnesia (RA) the doctor usually means they are not able to recall incidents or things they have learned before the injury or the disease began. Incidents that occurred closer to the time of the injury or disease, and things in the more distant past are not completely forgotten. (In extreme cases, the individual may completely forget who he or she is, but that is rare.) For example: someone in an automobile accident may have hit their head on the dashboard and although they can remember what happened the day before the accident, the day of the accident is a blank. This is the way the brain deals with some trauma, blocking out incidents that may be too painful to recover.
The areas of the brain most commonly affected in RA are the diencephalons, temporal lobes and the hippocampus. These areas work with episodic (autobiographical) and declarative memory (facts and knowledge).
- The hippocampus’ main function is take short-term memory and move it to long-term. It deals largely with memory consolidation, in particular episodic memory. Amnesic patients with damage to the hippocampus are able to understand concepts, but not personal information.
- Aside from helping to consolidate memory with the hippocampus, the temporal lobes are extremely important for understanding basic concepts (semantic) and factual memory processing. When there is damage to this region of the brain a patient can experience problems with verbal communication and comprehension, and experience long-term memory impairment. If the right side of the temporal lobe, in particular, is effected the patient experiences difficulty in naming objects, verbal memory and non-verbal activities such as music and drawing.
- The role of the diencephalon and the surrounding areas in memory is not very well understood, but this structure does appears to be involved in remembering personal emotions, time, places and things (episodic memory) recall.
Episodic and semantic memories make up the declarative (or explicit) memory, one of the two major memory divisions referring to memories that can consciously be recalled, such as facts and knowledge. It’s counterpart, known as non-declarative (or procedural) memory refers to unconscious memories such as skills (like riding a bicycle).
Memory loss can also be selective or categorical, manifested by a person’s inability to remember events related to a specific incident or topic, such as a recent car accident. The good news is that the wonders of the workings of the human brain allow plasticity to take over and reroute the connections to circumvent the damaged areas. In this way the brain learns to become independent of the damaged hippocampus, to a certain extent.
It is very rare to find stable RA, since improvement generally takes place among patients.
I am Ron White, two-time USA Memory Champion. The workings of the human brain are complicated and interesting, and I enjoy bringing you new information to help understand its workings.
Sources:
Wikipedia — Memory consolidation: http://en.wikipedia.org/wiki/Memory_consolidation; declarative memory: http://en.wikipedia.org/wiki/Declarative_memory;
The Human Memory — Retrograde Amnesia: http://en.wikipedia.org/wiki/Retrograde_amnesia
Memory Loss & The Brain: http://www.memorylossonline.com/glossary/retrogradeamnesia.html
