Known for decades as patient H.M., Henry Molaison was familiar, indeed dear, to neuroscientists. In 1953, epilepsy surgery to remove a tiny part of his brain left him forever unable to acquire new facts and store them. His case gave the field its first solid evidence that the hippocampus was involved in memory (see Scoville and Milner, 1957 ). During Molaison's life, MRI scans gave low-resolution views of his brain after surgery, but could not resolve crucial details about the borders of the lesion or the underlying cellular structure of his medial temporal lobe. When Molaison died in 2008, scientists preserved, froze, and thinly sliced his brain. From the resulting images, researchers led by Jacopo Annese at The Brain Observatory, San Diego, in collaboration with Suzanne Corkin at the Massachusetts Institute of Technology, Cambridge, have digitally reconstructed a detailed three-dimensional map of his brain and now report in the January 28 Nature Communications that more of the hippocampus remained than had been believed.
"The study of H.M. inaugurated the modern era of memory research," said Larry Squire, University of California, San Diego, who was not involved in the project. "With a case as important as this, we are going to want to know as much as we can about his brain."
Henry Molaison was just 10 years old when his seizures started. By age 27, in 1953, they were disruptive enough that doctors removed the affected portions of his brain: the medial temporal lobe structures, including part of the hippocampus. After the surgery, it quickly became apparent that he had lost the ability to form new declarative memories—ones involving facts and knowledge—though he retained his attentional and working memory capacity, as well as his intellectual abilities and personality. The surgeon's sketches approximated the removed areas, but not their true extent. With advances in brain MRI, Corkin's group later estimated that the resection included the medial temporal polar cortex, most of the amygdaloid complex, most if not all of the entorhinal cortex, and much of the hippocampus, including the dentate gyrus (see Corkin et al., 1997).