Researchers at The Brain Observatory in San Diego have embarked on a quest to help illuminate the meaning of a mysterious language engraved within a 2,401-page book. The inscriptions are those of neuroscience and the pages are brain slices. Two-thousand four-hundred and one slices of brain.
The original owner of this brain was a man commonly known to the public as H.M. These initials were bestowed upon him by the medical community in order to keep his identity separate from his pathology. Now, six years after his passing, H.M.’s true identity has reached the world wide web. His name was Henry.
The fact of the matter is, H.M. was much more than a specimen; it is his personal experience that actually makes his case so interesting. H.M. was only twenty-seven years old in the 1950s when he decided to undergo a radical lobotomy in an effort to treat an obdurate case of epilepsy. Epilepsy takes many forms and is still quite mysterious even to the most skillful of scientists. For our purposes, however, it is characterized by the long-term recurrence of seizures. The surgeon operating on H.M. removed a structure in the brain known as the medial temporal lobe including the hippocampus.
Several interesting occurrences arose after this surgery. For one, H.M.’s seizures were drastically reduced. However, this triumph came at a high price. H.M. began experiencing, and continued to experience, several types of amnesia for the rest of his life.
Amnesia is a form of memory loss. H.M. endured retrograde amnesia, meaning he was no longer able to recall memories from his life immediately before the procedure. In this form of amnesia, the most recent memories are completely lost and prior memories become more and more accessible as one attempts to recall further and further into the past. In H.M.’s particular case, he could not remember the year prior to his lesion.
However, H.M. experienced an even more debilitating form of amnesia: anterograde amnesia. This form of amnesia involves memory loss sustained after the surgery. For the rest of his life, H.M. was unable to form new declarative memories. Declarative memories include learning and storing memories of things like facts, events and the names of people. Interestingly enough, H.M. was still able to learn and retain new skillsets, like those involving motor coordination.
Up until recently, scientists only had sketches drawn by H.M.’s surgeon to document the areas of the brain which were either lesioned or left intact. In the 1990s, with the advent of neuroimaging, scientists were able to scan the preserved brain and discovered that, unbeknownst to the original surgeon, a portion of the hippocampus was inadvertently spared.
It is commonly known, through thousands of studies stemming from the original work with H.M., that the hippocampus and its connections to the cortex are largely responsible for memory function. Discovering the mistake in the surgeon’s documentation actually makes a lot of sense in light of H.M.’s experience with only partial memory loss, since only parts of the hippocampus, along with a connecting area known as the entorhinal cortex, were actually removed.
Scientists at The Brain Observatory in San Diego created the 0.7-millimeter slices utilizing a microtome to cut through the cryogenically preserved brain and created a catalog of serial photographs in order to reconstruct a high resolution 3-dimensional image of his brain. Researchers hope to utilize the model to further understand the mechanisms underlying H.M.’s pre- and post-surgery predicaments and to better diagnose neurological disorders in the future.
