, 2004). Brain imaging studies confirm that those factors include the efficiency of processes unrelated to the underlying cause of amnesia, such as the subsequent neurological regeneration of nerve fibers in particular (Staniloiu & Markowitsch, 2010). As predicted, volumes of animal studies and research involving testing individuals suffering from retrograde amnesia have subsequently identified several specific regions and structures as being involved in the development of retrograde amnesia that are completely distinct from the hippocampal regions implicated in connection with anterograde amnesia. In particular, Broca's Area and Wernicke's Area have been identified in that regard (Sadek, White, Taylor, et al., 2004). The other principal importance of these findings has to do with their roles of memory in human speech and language (James & MacKay, 2001).

Retrograde amnesia is often seen in connection with injury to regions of the temporal lobe and the right temporo-prefrontal cortices (Staniloiu & Markowitsch, 2010), areas of the brain that are closely related to two specific types of memory: declarative and episodic memory (James & MacKay, 2001). Those observations would be entirely consistent with the evidence that individuals suffering from retrograde amnesia typically experience no disruption of procedural memories (such as how to drive or wash themselves) or of semantic memory (such as how to use language and understand the meaning of words in their existing vocabulary). In that regard, some of the more interesting research suggests that, unlike other forms of amnesia, the extent to which individuals suffer (and are unable to recover) from retrograde amnesia depends partially on factors other than the nature, location, and extent of the actual damage to the regions of the brain involved. Instead, the degree of retrograde amnesia and its resistance to recovery also depend substantially on factors such as the strength and frequency of use of the affected knowledge prior to the onset of retrograde amnesia (Meeter & Murre, 2004).

Moreover, the fact that different types of memories...

Specifically, longer-term, older lost memories tend to be more recoverable and they are recovered more quickly (when they are recovered) than newer long-term memories (James & MacKay, 2001). That has been interpreted as being a function of the strength of neural connections attributable to more frequent use and to the process of reconsolidation of memories associated with repeated use (James & MacKay, 2001; Meeter & Murre, 2004).
Conclusion

Retrograde amnesia has long been identified as affecting different areas of the brain than those typically associated with other forms of amnesia, such as anterograde amnesia in particular. Whereas the latter is generally a function of damage to the hippocampal region, the former is a function of damage to the prefrontal cortices and other regions linked to speech and language. However, in addition to these regional distinctions, there is also evidence that retrograde amnesia and the extent of recovery is also substantially a function of factors not related to the nature of the damage to the affected regions. In that regard, the strength of memories prior to onset of amnesia symptoms and the frequency of their use are important, as are idiosyncratic differences seen in individuals with respect to metabolic and nerve tissue regenerative processes.

References

James, L.E. And MacKay, D.G. "H. M., Word Knowledge, and Aging: Support for a New Theory of Long-Term Retrograde Amnesia." American Psychological

Society, Vol. 12, No. 6 (2001): 485 -- 492.

Meeter, M. And Murre, J.M. "Consolidation of Long-Term Memory: Evidence and Alternatives." Psychological Bulletin, Vol. 130, No. 6, (2004): 843 -- 857.

Sadek, J.R., White, D.A., Taylor, K.I., et al., "Retrograde Amnesia in Dementia:

Comparison of HIV-Associated Dementia, Alzheimer's Disease, and Huntington's Disease." Neuropsychology, Vol. 18, No. 4 (2004): 692 -- 699.

Staniloiu, A. And Markowitsch, H.J. "Searching for the Anatomy…