Patient HM

Patient H.M Memory

Scoville localised his epilepsy as stemming from the medial temporal lobes and suggested removing these structures, including the hippocampus. Scoville had no idea what the function of the hippocampus was. After the surgery, HM no longer suffered from seizures, but his memory was significantly impaired.

Fig. 1 After surgery Patient HM developed retrograde amnesia but some other types of memory remained intact

H.M. Retrograde Amnesia

His short-term memory remained. However, his long-term memory became non-existent. He could not form any new memories of events, so for HM, time stopped in 1953, when he was 27. He could not remember anything about his daily life, such as where he lived, who cared for him, what he ate for his last meal, or how old he was.

For 55 years, HM participated in many experiments, mainly at the Massachusetts Institute of Technology. He learned some new motor skills, such as drawing a figure by looking at its reflection in a mirror. He never got tired of doing memory tests because they always seemed new to him. He enjoyed crossword puzzles and could repeat the same puzzle if the words were erased, as the puzzle was new to him each time.

Here are some examples of experiments in which HM participated:

• Recall tasks to see if he could recall memories/events of childhood and adulthood (before the surgery).

H.M. Impaired and Intact Types of Memory

• Tests measure other cognitive skills such as IQ, general knowledge, and perception. It was found that his personality remained similar, his IQ was not impaired, and his language and perception skills were largely unaffected, except for his sense of smell which was slightly impaired.

• Maze task: this is a task where you have to trace the correct route from the start to the finish point. HM attempted to do this task, using the same maze to see if he would be able to remember the correct route.

• Mirror star tracing task: This is a task to trace a star. In this task, participants cannot look directly at their hands. Instead, they have to look into a mirror to see their hand. Multiple trials were done to see if he learned the skill after practising it numerous times. HM improved at star tracing, making fewer mistakes each time he attempted the task, even though he could not remember doing the task.

HM even learned how to play tennis, even though he could not remember learning. This and his improvement in the mirror star tracing task shows his procedural memory was still intact.

What can we learn from research on HM?

Patient HM's results support the following conclusions:

• The hippocampus is vital for encoding short-term memories into long-term memories.
• There are different systems for retrieving and making long-term memories.
• There are different types of memories.
• Different brain regions are responsible for procedural and semantic memories.

Evaluation of Research on Patient HM

Multiple tests were used to measure different types of memories and cognitive skills. The tasks HM was asked to do had high reliability as they were tried-and-tested memory puzzles. Also, HM showed consistent results in studies with different researchers. Major advancements in memory research could be achieved because of HM.

Patient H.M. Controversy

Although the tests used have been established as reliable tools, the surgery that H.M. had and never can be replicated therefore, it is difficult to establish how valid the results are. As the study cannot be replicated the reliability of the study are difficult to establish.

Since the original research has been published several books and articles have been published. These books and articles have been heavily criticised and have sparked controversy over H.Ms case, such as ethical issues.

Patient H.M. Ethics

HM gave consent to participate in the studies each time they were explained to him over the next 50 years. There is some controversy over the ethics of patient HM, such as whether HM was able to give proper informed consent. This is due to his memory impairments.

HM took part in an experiment that involved administering electric shocks. This was stopped because the researcher noted that he was tolerant of them. However, researchers were respectful of HM. His real name was not revealed to the public until after his death. This could have potentially caused psychological and physical harm.