from traumatic experiences such as World War II. As aforementioned however, an etiology of psychogenic amnesia is controversial as causation is not always clear (see above paragraph), and both elements of psychological stress and organic amnesia may be present among cases. Often, but not necessarily, a premorbid history of psychiatric illness such as depression is thought to be present in conjunction to triggers of psychological stress. Lack of psychological evidence precipitating amnesia doesn't mean there isn't any, for example trauma during childhood has even been cited as triggering amnesia later in life, but such an argument runs the risk of psychogenic amnesia becoming an umbrella term for any amnesia of which there is no apparent organic cause. Due to organic amnesia often being difficult to detect, defining between organic and psychogenic amnesia is not easy and often context of precipitating experiences are considered (for example, if there has been drug abuse) as well as the symptomology the patient presents with. Psychogenic amnesia is supposed to differ from organic amnesia qualitatively in that retrograde loss of autobiographical memory while semantic memory remains intact is said to be specific of psychogenic amnesia. Another difference that has been cited between organic and psychogenic amnesia is the temporal gradient of retrograde loss of autobiographical memory. The temporal gradient of loss in most cases of organic amnesia is said to be steepest at its most recent premorbid period, whereas for psychogenic amnesia the temporal gradient of retrograde autobiographical memory loss is said to be quite consistently flat. Although there is much literature on psychogenic amnesia as dissimilar to organic amnesia, the distinction between neurological and psychological features is often difficult to discern and remains controversial. Diagnosis Functional assessment of brain activity can be assessed for psychogenic amnesia using imaging techniques such as fMRI, PET and EEG, in accordance with clinical data. Some research has suggested that organic and psychogenic amnesia to some extent share the involvement of the same structures of the temporo-frontal region in the brain. It has been suggested that deficits in episodic memory may be attributable to dysfunction in the limbic system, while self-identity deficits have been suggested as attributable to functional changes related to the posterior parietal cortex. To reiterate however, care must be taken when attempting to define causation as only ad hoc reasoning about the aetiology of psychogenic amnesia is possible, which means cause and consequence can be infeasible