Editing Retrograde amnesia (section)

== Types ==
[[File:Types of Retrograde Amnesia Flowchart.svg|thumb|upright=2|Types of RA can be divided into two main categories: temporally graded RA and pure forms of RA. Individuals with pure forms of RA like focal, isolated, and pure RA do not have anterograde amnesia (AA).]]

=== Temporally graded RA ===
Memory loss in patients with temporally graded RA strongly follows [[Ribot's law]], meaning that one will experience more memory loss for events closer to the injury or disease onset.<ref name="Wixted_2004" /> This type of RA is commonly triggered in individuals with [[Korsakoff syndrome]] due to a combination of long-term alcohol use and [[Wernicke encephalopathy]].<ref>{{cite book | vauthors = Bauer RM, Asken B | veditors = Morgan JE, Ricker JH | chapter = Chapter 28: The Three Amnesias |date= 2008 | doi = 10.4324/9781315537511-51 | title = Textbook of Clinical Neuropsychology | edition = 2nd | pages = 678–700 | location = New York, NY | publisher = Rutlidge |isbn = 978-1-351-98599-4 }}</ref> Debate has risen about why this temporal gradient forms in the first place. Initial theories proposed that the [[hippocampus]] and [[medial temporal lobe]] are not nearly as important for long-term memories compared to short-term memories.<ref name="Lafleche_2011" /> As memory processing occurs in the brain over time, neocortical regions can directly communicate with each other, so they do not rely as heavily on the hippocampus for long-term memory storage.<ref name="Lafleche_2011" /> Therefore, if an individual experiences RA that damages the hippocampus, they will lose more short-term memories according to this theory. However, this theory has been challenged by the multiple-trace theory, which claims that the brain develops a hippocampal trace each time a memory is retrieved.<ref name="Lafleche_2011" /> Since more hippocampal traces are present for older memories, it is easier for older memories to remain intact when RA occurs.<ref name="Lafleche_2011" />

=== Focal, isolated, and pure RA ===
An absence of anterograde amnesia (AA) characterizes pure forms of RA, which fall into three main categories: focal, isolated, and pure RA.<ref name="Lafleche_2011" /> Slight differences in the use of these terms to describe a pure form of RA are summarized below:
{| class="wikitable"
|+Pure Forms of RA
!width=42%|Focal RA
!width=29%|Isolated RA
!width=29%|Pure RA
|-
|Focal RA generally results from neurological problems like epilepsy and is characterized by memory loss prior to – but not after – injury or disease onset.<ref>{{cite journal | vauthors = Sehm B, Frisch S, Thöne-Otto A, Horstmann A, Villringer A, Obrig H | title = Focal retrograde amnesia: voxel-based morphometry findings in a case without MRI lesions | journal = PLOS ONE | volume = 6 | issue = 10 | pages = e26538 | date = 2011-10-19 | pmid = 22028902 | pmc = 3197527 | doi = 10.1371/journal.pone.0026538 | bibcode = 2011PLoSO...626538S | veditors = de Beeck HP | doi-access = free }}</ref> When an individual experiences focal RA, a combination of their episodic and semantic memories may be affected.<ref name="Wheeler_2001">{{cite journal | vauthors = Wheeler MA, McMillan CT | title = Focal retrograde amnesia and the episodic-semantic distinction | journal = Cognitive, Affective & Behavioral Neuroscience | volume = 1 | issue = 1 | pages = 22–36 | date = March 2001 | pmid = 12467101 | doi = 10.3758/CABN.1.1.22 | s2cid = 20269516 | doi-access = free }}</ref> In one case study, a middle-aged female experienced focal RA after significant head trauma.<ref name="Wheeler_2001" /> Although she could be re-taught information from her past, these memories were not episodic, but rather, semantic.<ref name="Wheeler_2001" /> With focal RA, the details of a patient's life prior to amnesia onset can be reintroduced, but they are unable to recall how they perceived the experience.<ref name="Wheeler_2001" />
|Isolated RA is usually associated with a visible [[Thalamus|thalamic]] lesion.<ref name="Miller_2001">{{cite journal | vauthors = Miller LA, Caine D, Harding A, Thompson EJ, Large M, Watson JD | title = Right medial thalamic lesion causes isolated retrograde amnesia | journal = Neuropsychologia | volume = 39 | issue = 10 | pages = 1037–46 | date = 2001 | pmid = 11440756 | doi = 10.1016/s0028-3932(01)00041-0 | s2cid = 18021762 }}</ref> Similar to other forms of RA, the inability to recall past information characterizes the isolated form.<ref name="Miller_2001" /> In one case study, a middle-aged man, identified as JG, had a thalamic lesion which expanded as he grew older.<ref name="Miller_2001" /> This lesion growth induced his isolated RA, resulting in both autobiographical memory loss and the inability to recognize information from popular culture.<ref name="Miller_2001" />
|Pure RA (PRA) is caused by a range of factors such as vascular diseases, encephalitis, and head injuries.<ref name="Lucchelli_1998">{{cite journal |vauthors=Lucchelli F, Muggia S, Spinnler H |date=1998 |title=The Syndrome of Pure Retrograde Amnesia |journal=Cognitive Neuropsychiatry |volume=3 |issue=2 |pages=91–118 |doi=10.1080/135468098396189}}</ref> It is often confused with peritraumatic amnesia that commonly follows mild concussions, but the severity and duration of PRA differs from that of peritraumatic amnesia.<ref name="Lucchelli_1998" /> Current discussion in neuropsychiatry literature centers on whether PRA is possibly [[Psychogenic disease|psychogenic]] in nature.<ref name="Lucchelli_1998" />
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