difficulties and ultimately develop RA. However, some of the drawbacks of using Korsakoff patients to study RA is the progressive nature of the illness and the unknown time of onset. Infections Infections that pass the blood–brain barrier can cause brain damage (encephalitis), sometimes resulting in the onset of RA. In the case of patient 'SS', the infection led to focal or isolated retrograde amnesia where there was an absence of or limited AA. Brain scans show abnormalities in the bilateral medial temporal lobes, including two thirds of the hippocampal formation and the posterior part of the amygdala. Surgery Henry Molaison had epilepsy that progressed and worsened by his late twenties. The severity of his condition caused him to undergo surgery in an effort to prevent his seizures. Unfortunately, due to a lack of overall known neurological knowledge, Molaison's surgeons removed his bilateral medial temporal lobe, causing profound AA and RA. The removed brain structures included the hippocampus, the amygdala, and the parahippocampal gyrus, now called the medial temporal lobe memory system. HM was one of the most studied memory cases to date and started the examination of neurological structures in relation to memory. Patients who have RA due to surgery are "P.B." and "F.C." who had unilateral removal of the medial areas in the left temporal lobe. Controlled induction Clinically induced RA has been achieved using different forms of electrical induction. Electroconvulsive therapy (ECT), used as a depression therapy, can cause impairments in memory. Tests show that information from days and weeks before the ECT can be permanently lost. The results of this study also show that severity of RA is more extreme in cases of bilateral ECT rather than unilateral ECT. Impairments can also be more intense if ECT is administered repetitively (sine wave simulation) as opposed to a single pulse (brief-pulse stimulation). Electroconvulsive shock (ECS): The research in this field has been advanced by using animals as subjects. Researchers induce RA in rats, for example, by giving daily ECS treatments. This is done to further understand RA. Brain structures The most commonly affected areas are associated with episodic and declarative memory such as the hippocampus, the diencephalon, and the temporal lobes. The hippocampus deals largely with memory consolidation, where information from the working memory and short-term memory is encoded into long-term storage for future retrieval. Amnesic patients with damage to the hippocampus are able to demonstrate some degree