Henry G. Molaison, known in the medical literature as H.M., had parts of the hippocampus in his brain removed in 1953 at the age of 27, following increasingly severe seizures that couldn't be treated effectively with medications.
"During life, H.M. was the best-known and possibly the most studied patient in modern neuroscience," Jacopo Annese of the University of California, San Diego, and his co-authors conclude in Tuesday's issue of the journal Nature Communications.
After the surgery, Molaison had difficulty forming long-term memories of facts, faces and experiences. His willingness to participate in testing led to a range of contributions to science during his life and after his death in 2008 at the age of 82 from respiratory failure.
The latest is a digital 3D reconstruction of his brain based on thin tissue slices of his brain.
Annese said the 3D model uses virtual dissection to examine the original surgery. In the study, the researchers say the reconstruction revealed several findings, including pathology in the deep white matter and a small lesion with clearly defined edges in a frontal lobe that hadn’t been described before.
They say neurosurgeon William Beecher Scoville "reached beyond and below the posterior hippocampus." A circuit that acts as a gateway to the hippocampus from the brain's outer layer to support the consolidation of long-term memories was also likely severely compromised during treatment.
Brain structures that were spared could also validate Montreal-based McGill neuroscientist Brenda Milner and her team’s observations of Molaison’s preserved abilities to learn perceptual tasks, Annese’s team said, while microscopic studies of his remaining tissue in the hippocampus raise questions about how well it functioned.
Pathology observations of his white matter suggest changes acquired from medical conditions, including hypertension.
The researchers said closer study is needed to learn more about aging-related abnormalities that happened independently of Molaison’s surgery.
Molaison also lacked the ability to report internal states such as pain, hunger or thirst, which was attributed to the removal of his amygdala.
The study was funded by the U.S. National Science Foundation, the Dana Foundation Brain and Immuno-Imaging Award, and by contributions from viewers of the web broadcast of the dissection.