‘HM, an Unforgettable Amnesic’ (New York Times, 2008). Critically evaluate the contribution made by HM and other key patient studies to our understanding of human Long-Term Memory. In particular, refer to patient studies of the organisation of conceptual knowledge (e. g. semantic memory) and episodic memories. ‘Long-term memory is a system for permanently storing, managing, and retrieving information for later use. Items of information stored as long-term memory may be available for a lifetime’. (Webster’s New World™ Medical Dictionary, 3rd Edition, 2008).
Long term Memory can be divided into two main subdivisions: Explicit and implicit memory; Explicit memory is the deliberate recall of information that one recognizes as a memory. Implicit memory is the influence of recent experience on behaviour without realizing one is using memory. Tulving (1978) proposed that Long-term Memory can be categorised into three main groups; semantic, episodic and procedural memory. Semantic memory is involved with storing ideas, meaning and concepts. It is conscious and declarative and is used in retrieving general knowledge as well as the meaning of words.
Episodic memory is a conscious and declarative process involved with storing memories of particular events in your life. Procedural memory involves the unconscious and is not declarative. It is responsible for knowing how to do processes such as riding a bike. (Mc Leod, 2010) Patient studies such as HM, EP and others have been instrumental in understanding long term memory. Before these not much was known about how and where long term memory was stored. It was only in the 1950’s after patient HM that the hippocampus was associated with memory.
The hippocampus is located inside the medial temporal lobe, beneath the cortical surface of the brain and HM proved the hippocampus was instrumental to the storage and function of long term memory. In 1953 a patient known as HM had brain surgery when he was 27 years old. HM suffered from severe epilepsy. Surgeons removed large portions of his medial temporal lobes in an attempt to control his epileptic seizures. Although HM’s epileptic seizures were reduced and his epilepsy was controlled, significant problems were seen in his memory storage and functions as a side effect.
Although his short term memory still functioned properly, it appeared that his long term memory had been significantly damaged. (White, 2004) He showed great difficulty when forming new long term memories and demonstrated basically no knowledge of current affairs as he appeared to forget every news item moments after he heard or read about it. It appeared he was unable to retain any information. He also appeared to have no recollection of recent events such as monumental things like the death of his father that had transpired within the year preceding his surgery.
Although he could remember individuals he had known in the past, specifically in the past year. HM also could not recall individuals he had met recently and was unable to store information about new people he encountered who remained strangers to him throughout his life. In hindsight HM ‘appeared ‘cognitively’ normal due to the fact he was able to learn and remember perceptual and motor skills although in cases he needed reminding of what he was able to do’ (Mc Leod, 2010). He developed anterograde amnesia which proved that the hippocampus is vital for the formation of long term memories.
Anterograde amnesia is a form of amnesia in which sufferers loss their ability to form new long term memories. The fact that HM could not recall events that had transpired in the past year can be considered as evidence that the transfer of memory into long term storage takes place over several years with the hippocampus being necessary for its retrieval in the first year or so. (White, 2004) Patient EP was also a prominent figure in helping to understand the workings of long term memory. In 1992, after suffering from herpes simplex encephalitis at the age of seventy EP became profoundly amnesiac.
His amnesia seemed to worsen after the time of his illness. At first he appeared to have symptoms similar to those of the flu whilst experiences moment of memory loss in which he periodically would forget family members names. His memory then disintegrated even more and by June of 1993 although medically stable he had suffered from profound memory impairment which was permanent. Despite this however EP’s physical appearance remained intact. However he seemed unable to retain any information properly and often became confused, repeating his routines throughout the day.
In a day EP may repeat his morning activities including getting up and eating breakfast as much as three times a day according to his wife. Although able to wash and shave he sometimes required reminders from his wife. This shows how his motor memory skills were still functioning implicating that like HM he was an anterograde amnesiac suffering from memory loss in events happening after his illness. However he also has been considered experiencing reterograde amnesia as he had trouble emembering famous people and events that had occurred before the 1950’s although able to recall past memories such as his childhood and his experiences of World War 2. (Journal of Neuroscience, 2000). There were many similarities between HM and EP’s condition. After further medical examination of HM (Corkin et al. 2007) it appeared that EP’s damage in the temporal lobe lesion including the hippocampus was more severe. Another study which greatly contributed to our understanding of human long term memory was that of a patient known as DC. DC was a 47 year old doctor diagnosed with paranoid schizophrenia.
Following a law suit in 1950 which dealt with his homicidal attack on his wife he was admitted to hospital. In 1954 an operation which involved, ‘a bilateral medial temporal-lobe resection combined with orbital undercutting was carried out in an attempt to counter his schizophrenic behaviour’. (Scoville & Milner 2012). Although when examined it appeared that his schizophrenic tendencies were reduced, DC suffered from severe memory loss. This was evident immediately after his operation when he was no longer able to recall hospital staff and could not find his bed.
Upon examination he showed similar patterns of memory loss as that to patient HM. Although his I. Q. remained the same he was no longer able to hold information for longer that a few moments. He was unable to remember the names of hospital life, where he was or information he had been told moments before. Like HM he was able to recall his memories from the past however DC had no recollection of having the operation although the overall process had taken up to a year including the time he had been in hospital. This showed how the transfer of memories from short term to long term takes place over a number of months. Scoville & Milner 2012) Similar to DC and yet again HM was the case of a patient known as MB. MB was admitted to Connecticut State hospital in 1951 to treat manic depression. She underwent a radical bilateral medial temporal-lobe resection similar to DC and the pattern of experiencing memory loss began again. It appeared that she had suffered from a substantial amount of memory impairment when examined by Mr. Borganz approximately one year later. She was unable to remember the past three years of her life although like HM and DC she showed no signs of decreased intelligence.
When further examined in 1955 it was revealed that she was unable to remember her dwelling of the past three and a half years and was not familiar with the surroundings. She also was not able to retain information. She was however able to recall memories from the past which centred on her early life. (Scoville & Milner 2012) Patient’s EP, HM, DC and MB were all crucial to our understanding of how long term memory in humans works. Through findings from their examinations it revealed that the hippocampus was vital in the storage and transfer of long term memory.
It was only because of HM that memory was associated with the hippocampus in general. Through examining these patients it also lead to the conclusion that long term memory and short term memory are stored in completely different parts of the brain as in HM and the patients above their short term memory functioned normally after the memory loss. In conclusion, one can state that without patients such as HM, EP, DC and MB our understanding of long term memory in humans would be limited.
References
1. Profound Amnesia After Damage to the Medial Temporal Lobe: A Neuroanatomical and Neuropsychological Pro?le of Patient E. P; Lisa Stefanacci, Elizabeth A. Buffalo, Heike Schmolck and Larry R. Squire; The Journal Of Neuroscience; 2012 2. Loss of recent memory after bilateral hippocampal lesions; William Beecher Scoviille and Brenda Milner; group. bmj. com; 2012 3. What Happened? Alcohol, Memory Blackouts, and the Brain; Aaron M. White; Vol. 27 No. 2; 2003 4. Imaging recollection and familiarity in the medial temporal lobe: a three-component model; Trends in Cognitive Sciences; Rachel A. Diana, Andrew P. Yonelinas and Charan Ranganat; Elseivier Ltd. 2007 5. Principals of Cognitive Pyschology; Michael Eysenck; 2nd Edition; 2001
