Neuroscience took a big step forward when it scanned and sliced one of the most famous brains it has ever studied.
The brain of H.M., now revealed to be Henri Gustav Molaison, has been under the custody of the University of California San Diego, ever since Molaison died in 2008 at the age of 82. Researchers froze his brain in a formaldehyde buffer to which sucrose was gradually added.
A year after, in 2009, the research team, led by Dr. Jacopo Annese of the Brain Observatory, froze the entire brain as a single block, and began cutting it into 2,401 slices, for use in further research. The entire process took 53 hours. Annese said he did not sleep for three days, and he had students stay with him in shifts to make sure that he stayed awake. "There was always one person next to me, and if I looked like I was phasing out or missing a slice, the code word was 'prosciutto'," he said. "It was probably the most engaging, most exciting thing I've ever done."
The procedure was live-streamed starting on December 2, 2009, and was watched by about 400,000 people. The slicing was very tedious business. The brain needed to be frozen and sliced at a consistent -35 degrees Centigrade. Any slight increase in temperature can cause the brain to soften and more prone to being gouged. Any slight decrease in temperature can make the brain shatter.
Molaison was only 27 years old in 1953 when he underwent an experimental surgery to relieve him of his chronic epileptic seizures. When he was 10 years old he began to experience minor epileptic seizures, which had gotten worse by the time he was 15. The surgery, led by neurosurgeon William Beecher Scoville of Hartford Hospital, removed the hippocampus, which is crucial for storing memory, and parts of his left and right medial temporal lobes.
The surgery cured Molaison of his epilepsy. However, he was unable to remember anything that happened to him for the rest of his life. He was able to retain only those memories he acquired before the moment of the surgery. In effect, he was unable to hold down a job or live on his own. Although he remained articulate and intelligent, with a measured IQ of above-average, and his motor skill learning and other cognitive skills remained intact, his amnesia served to relegate him to a life of dependence on the care and attention of others.
"Right now, I'm wondering, have I done or said anything amiss?" He was quoted as saying. "You see, at this moment everything looks clear to me, but what happened just before? That's what worries me. It's like waking from a dream. I just don't remember."
In 1984 Molaison underwent a series of CT scans for his brain, and in 1992 and 1993 magnetic resonance imaging was used to achieve a better scan.
Findings of these scans published in the online journal Nature say: "MRI scans revealed that the lesion was symmetrical as Scoville had planned, but was less extensive than his estimate. It included the medial temporal polar cortex, most of the amygdaloid complex and entorhinal cortex (EC), and about half of the rostro-caudal extent of the intraventricular segment of the hippocampal formation (dentate gyrus, hippocampus and subiculum). Portions of the ventral perirhinal cortex were spared, and the parahippocampal cortex appeared largely intact. The frontal, parietal and occipital cortices had a generally normal appearance, and neocortical atrophy was slight and consistent with H.M.'s age."
Molaison has pledged his brain to science, and it is probably one of the most-studied in the field. Now, researchers at the UC San Diego have used the 2,401 slices of the brain to create a 3D model, in microscopic detail, to help shed light on the anatomical structures that are responsible for the creation and storage of memory. The end-goal of this project is for Molaison's brain to be showcased in the first-ever high-resolution, three-dimensional atlas of the human brain, and it's free-access as well, inviting collaborations for mind-mapping and further study.
