January 29, 2014
Researchers Digitize Neuroscience’s Most Famous Brain
redOrbit Staff & Wire Reports - Your Universe Online
For decades, Molaison – known simply as H.M. in thousands of scientific papers – cooperated with researchers who wanted to better understand his unusual memory deficit in hopes of learning more about how the brain creates a record of people, facts and experiences. The unfortunate purity and severity of H.M.’s memory impairment, along with his willingness to participate in continual testing, made his case uniquely influential, serving as the catalyst for over 50 years of scientific discoveries that radically changed scientists' understanding of memory function.
H.M.’s case was particularly significant because it provided the first conclusive evidence for the involvement of the hippocampus in forming new memories.
According to Smithsonian's Joseph Stromberg, William Beecher Scoville, who performed Molaison’s surgery in 1953, had removed large parts of H.M.’s medial temporal lobes (MTL), including the hippocampus. At the time of the surgery, conventional wisdom was that memory traces were distributed throughout the brain. But H.M. showed that certain parts of the brain are vital for specific memory functions, and doctors now know that if this structure is shutdown or removed, a person can’t form new memories of people, places, objects and events.
In December 2009, Jacopo Annese, PhD, at the University of California, San Diego, and his team dissected H.M.'s brain into 2,401 thin tissue slices, and preserved them cryogenically in serial order. While the brain was being sliced, the researchers collected an unabridged series of digital images of the surface of the block, corresponding to each tissue section. These images were archived and used to create a 3D microscopic model of H.M.’s whole brain.
The model contains clues to help understand the surgery performed in 1953, and the level of sampling and image quality afforded by this study represents a significant advance over the MRI scans performed on H.M. when he was alive, the researchers said.
"Our goal was to create this 3D model so we could revisit, by virtual dissection, the original surgical procedure and support retrospective studies by providing clear anatomical verification of the original brain lesion and the pathological state of the surround areas of H.M.'s brain," Annese said.
The study reveals a small, circumscribed lesion in the left orbitofrontal cortex that had been previously undiscovered, demonstrating the power of the technique. Based on the 3D geometry of the lesion and the type of the lobectomy that was performed in 1953, Annese said he believes the lesion was very likely created by Scoville during the surgery.
The digitized model of H.M.’s whole brain, and detailed 3D measurements of the medial temporal lobe (MTL) region, is described in a paper published online January 28 in the journal Nature Communications. A Google maps version of the slice featured in the paper (Figure 5) can be viewed here.