Causes
The causal explanation of RA is still under investigation, however, it is commonly associated with head injuries or traumas, Korsakoff syndrome, and individuals suffering from AA.
The Three main models used to explain RA assume that the hippocampus is one of the main areas of the brain used in memory consolidation. During consolidation, the hippocampus acts as an intermediate tool that quickly stores new information until it is transferred to the neocortex for the long-term. The temporal lobe, which holds the hippocampus, entorhinal, perirhinal and parahippocampal cortices, has a reciprocal connection with the neocortex. The temporal lobe is temporarily needed when consolidating new information, as the learning becomes stronger; the neocortex becomes more independent of the temporal lobe.
Studies on specific cases demonstrate how particular, impaired areas of the hippocampus are associated with the severity of RA. Damage can be limited to the CA1 field of the hippocampus, causing very limited RA for a duration of about 1 to 2 years. More extensive damage limited to the hippocampus causes temporally graded amnesia for a duration of 15 to 25 years. Another study also suggested that large medial temporal lobe lesions, that extends laterally to include other regions produces more extensive RA, covering 40 to 50 years. These findings suggest that density of RA becomes more severe and long-term as the damage extends beyond the hippocampus to surrounding structures.
It is important to note that the common studied causes of RA do not always lead to the onset of RA.
Read more about this topic: Retrograde Amnesia