She is a superb experimentalist with a strong conceptual orientation that allowed her to draw from her data deep insights about the organization of memory. It has provided broad evidence for the rejection of old theories and the formation of new theories on human memory, in particular about its processes and the underlying neural structures cf. This is a false-colour PET scan highlighting the limbic areas of the brain.
Yet at the end of testing, he had no recollection of having done the task before. This demonstration provided the first hint that there was more than one kind of memory in the brain and suggested that some kinds of memory motor skills must lie outside the province of the medial temporal lobe. For a time, it was rather thought that motor skills were a special case and that all the rest of memory is impaired in patients like H.
Later it became appreciated that motor skills are but a subset of a larger domain of skill-like abilities, all of which are preserved in amnesia. The demonstration of a fully preserved ability to learn the perceptual skill of mirror reading suggested a distinction between two broad classes of knowledge: Procedural memory refers to skill-based knowledge that develops gradually but with little ability to report what is being learned. In the years that followed, other preserved learning abilities began to be reported for amnesic patients, and the perspective shifted to a framework that accommodated multiple i.
As Endel Tulving wrote:. But even if we accept the broad division of memory into procedural and propositional forms Subsequently, the terms declarative and nondeclarative were introduced with the idea that declarative memory refers to the kind of memory that is impaired in H. Nondeclarative memory is an umbrella term referring to additional memory systems. These include systems that support skill learning, habit learning, simple conditioning, emotional learning, as well as priming and perceptual learning.
The structures with special importance for these kinds of memory include the basal ganglia, the cerebellum, the amygdala, and the neocortex. The starting point for these developments was the early discovery that motor skill learning was preserved in H.
This finding revealed that memory is not a single faculty of the mind and led ultimately to the identification of the multiple memory systems of the mammalian brain. A key insight about the organization of memory, and medial temporal lobe function, came with a consideration of his capacity to remember information that he had acquired before his surgery.
The first exploration of this issue with formal tests asked H. This important finding implied that the medial temporal lobe is not the ultimate storage site for previously acquired knowledge. The early descriptions of H. Similarly, about 10 years later it was remarked that there did not appear. Subsequently, a particular interest developed in the status of autobiographical memories for unique events, which are specific to time and place, and methods were developed to assess the specificity and the detail with which such recollections could be reproduced.
In the earliest efforts along these lines, as summarized by Suzanne Corkin Corkin, , H. It was concluded that H. The situation seemed to change further as H. In an update prepared nearly 20 years later Corkin, , H.
It was also said that he could not narrate a single event that occurred at a specific time and place. Essentially the same conclusion was reached a few years later when new methods, intended to be particularly sensitive, were used to assess H. These later findings led to the proposal that, whatever might be the case for fact memory, autobiographical memories, i. There are reasons to be cautious about this idea. In , new MRI scans of H.
These scans documented a number of changes since his first MRI scans from Corkin et al. These findings were thought to have appeared during the past decade, and they complicate the interpretation of neuropsychological data collected during the same time period.
Another consideration is that remote memories could have been intact in the early years after surgery but then have faded with time because they could not be strengthened through rehearsal and relearning.
In any case, the optimal time to assess the status of past memory is soon after the onset of memory impairment. Other work has tended to support the earlier estimates that H. Second, methods like those used recently to assess H. In these cases, autobiographical recollection was impaired when memories were drawn from the recent past but fully intact when memories were drawn from the remote past. Memory loss can sometimes extend back for decades in the case of large medial temporal lobe lesions though additional damage to anterolateral temporal cortex may be important in this circumstance.
In any case, memories from early life appear to be intact unless the damage extends well into the lateral temporal lobe or the frontal lobe. These findings are typically interpreted to mean that the structures damaged in H. For instance, he could add a memory about Jonas Salk by modifying his memory of polio. He died on December 2, Molaison was influential not only for the knowledge he provided about memory impairment and amnesia, but also because it was thought his exact brain surgery allowed a good understanding of how particular areas of the brain may be linked to specific processes hypothesized to occur in memory formation.
In this way, his case was taken to provide information about brain pathology , and helped to form theories of normal memory function. In particular, his apparent ability to complete tasks that require recall from short-term memory and procedural memory but not long-term episodic memory suggests that recall from these memory systems may be mediated, at least in part, by different areas of the brain.
Similarly, his ability to recall long-term memories that existed well before his surgery, but inability to create new long-term memories, suggests that encoding and retrieval of long-term memory information may also be mediated by distinct systems.
Nevertheless, imaging of Molaison's brain in the late s revealed the extent of damage was more widespread than previous theories had accounted for, making it very hard to identify any one particular region or even isolated set of regions that were responsible for HM's deficits. The study of Molaison revolutionized the understanding of the organization of human memory. It has provided broad evidence for the rejection of old theories and the formation of new theories on human memory, in particular about its processes and the underlying neural structures cf.
In the following, some of the major insights are outlined. Molaison's brain was the subject of an anatomical study funded by the Dana Foundation and the National Science Foundation. The aim of the project, headed by Jacopo Annese, of The Brain Observatory at UC San Diego , was to provide a complete microscopic survey of the entire brain to reveal the neurological basis of Molaison's historical memory impairment at cellular resolution.
On December 4, , Annese's group acquired brain slices, with only two damaged slices and 16 potentially problematic slices. The results of the study were published in Nature Communications for January The researchers found, to their surprise, that half of H. Additionally, a previously unexpected discrete lesion was discovered in the prefrontal cortex. These findings suggest revisiting raw data from behavioral testing [ citation needed ].
A three-dimensional virtual model of the brain allowed the dynamics of the surgery to be reconstructed; it was found that the brain damage above the left orbit could have been created by Dr. Scoville when he lifted the frontal lobe to reach into the medial temporal lobes. The article also describes the general neuropathological state of the brain via multiple imaging modalities.
Several pathological features were discovered, some severe, which had contributed to his cognitive decline. The digital atlas of HM's brain was made publicly available on the Internet free of charge; its "permanence on the web relies on contributions from users". Molaison's general condition has been described as heavy anterograde amnesia , as well as temporally graded retrograde amnesia. Since HM did not show any memory impairment before the surgery, the removal of the medial temporal lobes can be held responsible for his memory disorder.
Consequently, the medial temporal lobes can be assumed to be a major component involved in the formation of semantic and episodic long-term memories cf. Further evidence for this assumption has been gained by studies of other patients with lesions of their medial temporal lobe structures. Despite his amnesic symptoms, Molaison performed quite normally in tests of intellectual ability, indicating that some memory functions e.
However, for sentence-level language comprehension and production, Molaison exhibited the same deficits and sparing as in memory. Molaison was able to remember information over short intervals of time.
This finding provides evidence that working memory does not rely on medial temporal structures. It further supports the general distinction between short-term and long-term stores of memory.
Molaison's largely intact word retrieval provides evidence that lexical memory is independent of the medial temporal structures. In addition to his intact working memory and intellectual abilities, studies of Molaison's ability to acquire new motor skills contributed to a demonstrated preserved motor learning Corkin, In a study conducted by Milner in the early s, Molaison acquired the new skill of drawing a figure by looking at its reflection in a mirror Corkin, Further evidence for intact motor learning was provided in a study carried out by Corkin In this study, Molaison was tested on three motor learning tasks and demonstrated full motor learning abilities in all of them.
Experiments involving repetition priming underscored Molaison's ability to acquire implicit non-conscious memories, in contrast to his inability to acquire new explicit semantic and episodic memories Corkin, These findings provide evidence that memory of skills and repetition priming rely on different neural structures than memories of episodes and facts; whereas procedural memory and repetition priming do not rely on the medial temporal structures removed from Molaison, semantic and episodic memory do cf.
It would take years of study using animal models and great advancements in technology before the medial lobe memory system was fully understood, but Patient HM helped to lay the foundations of this vital research. In Milner published the results of a series of trials that she had conducted with Henry, which revealed one of her most notable discoveries. In the trials she had asked Patient HM to draw a line between two outlines of a five-pointed star while watching his hand and the page in a mirror.
Milner asked Henry to repeat this task several times on several different occasions. Each time Henry did not remember having completed the task before, yet his performance improved. This demonstrated that, although he was not conscious of it, Henry was able to learn new motor skills by repeated practice.
From these trials Milner was able to conclude that this form of memory, called motor learning, must be distinct from the system of memory that records new facts, faces and experiences. Henry was always supportive of the research that he enabled and said he was glad that he could be of help to others. In he gave his consent for his brain to be used in further research after his death, and this led to the establishment of Project HM.
When Henry died in , his brain was removed and scanned repeatedly using MRI. It was then sent to the Brain Observatory at the University of California. In scientists sliced the brain into 2, pieces, each just 70 micrometres millionths of a metre thick. Their aim was to create stained histological slides that would enable researchers to map the brain in new ways and connect individual anatomical structures with specific functions.
The dissection took 53 hours to complete and five blades were used in the process. Each slice was photographed and the images were posted online, and the whole procedure was streamed live on the internet.
Henry and his doctors could not have imagined the technology that would eventually be used to preserve his brain, nor could they have predicted the advances in neuroscience that would result from his operation, his condition and his generosity.
To read about how resection operations are done today and to hear a surgeon talk about how technology helps him operate, read our interview with Conor Mallucci.
Patient HM was an important case study for neurological research in the 20th century. Holly Story discovers how his life and his unique condition helped scientists to understand the brain Henry Gustav Molaison, known to the world as ‘Patient HM’, has been called . Aug 11, · A man known as HM provided the key to one of the mysteries of the human brain. Access to Henry was carefully restricted to less than researchers (I was honored to be one of them), but the MNI and MIT studies on HM taught us much of what we know about memory.