Amnesia is a partial or total loss of memory. It is usually caused after an event causing brain damage and has 2 major symptoms. The first, anterograde amnesia, is the inability to learn new, explicit information after trauma. The second, retrograde amnesia, is the inability to retrieve explicit information from time prior to trauma, with a temporal grading, meaning newer memories are more susceptible to loss (Psych 240 Lecture, 10-15-14). Amnesia has been the focus of countless hours of research, however, none have totally explained how it works. There are many questions about the specific brain structures involved in memory and amnesia and a number of studies have been conducted to try to answer this puzzling query.
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Patient HM was a man who experienced profound amnesia after removal of his medial temporal lobe to alleviate severe epilepsy and has provided many insights into the mechanisms of amnesia. This work revealed the importance of the amygdala and hippocampus, located in the medial temporal lobe, in explicit memory, a conscious recollection of declarative knowledge. However, his implicit memory, or memory for skills and procedural knowledge (Psych 240 Lecture, 10-15-14), was mostly intact. Numerous studies of HM across 30 years illustrated the importance of the hippocampus and amygdala in storing and retrieving explicit memories. (Ogden and Corkin, 1991). The studies of HM revealed, however, that amnesiacs could still learn some new facts and procedures. HM demonstrated a learning of tasks, however, he had no idea that he had learned it. One example is the tower of Hanoi experiment, in which subjects are asked to move a series of rings on pegs to create a stack with the largest ring at the top and the smallest at the bottom. While amnesiacs had no conscious recollection of completing the task, their performance increased over time as much as control subjects. This illustrates their ability to learn new procedural information, a part of implicit …show more content…
The information presented in the discussed studies supports the claim that the hippocampus and amygdala play an important role in memory and loss of memory via amnesia. The hippocampus plays a key role in explicit memory, including both episodic and semantic memory. Patients with damage to the hippocampus and surrounding structures experience difficulty in both remembering events leading up to the trauma and learning or remembering new information after trauma. These effects have been greatly studied in patient HM, who provided many key insights for psychologists. He demonstrated that the hippocampus is essential in both episodic memory and semantic memory. Patient HM does not remember anyone he met after his operation and has a very limited knowledge of events that occurred since then. He has a limited recognition of celebrities that became famous after his operation. He also seems to remember that his father passed away, but this could be a result of the memory becoming encoded in his procedural memory. He provided great insights into the human mind in many years of study. Additionally, other research indicated that the hippocampus is not involved in all memory. Kim and Faneslow showed that the hippocampus is involved in associative learning in rats, but has little role in long-term