From The New York Times:

WEEDSPORT, N.Y. — Adam Lepak looked over at his mother and said, “You’re fake.”

It was a Tuesday in July, late, and Cindy Lepak could see that her 19-year-old son was exhausted. Long days like this one, with hours of physical therapy and memory drills — I had a motorcycle accident, I hit my head and have trouble remembering new things, I had a motorcycle accident — often left him making these accusations.

“What do you mean ‘fake,’ Adam?” she said.

He hung his head. “You’re not my real mom,” he said. His voice changed. “I feel sorry for you, Cindy Lepak. You live in this world. You don’t live in the real world.”

Adam has Capgras delusion, which is a brain disorder resulting from brain damage. In Adam’s case, it was a motorcycle accident. The damage has occurred diffusely enough that people no longer recognize important people in their lives – their parents, spouse, or even themselves.

What is the primary cause of Capgras delusion? Of course, scientists argue. One of the most compelling theories, however, is that the connection between our facial recognition system in the fusiform gyrus in the left temporal lobe and our emotional system in the limbic area (Hirstein & Ramachandran, 1997). Therefore, we can recognize important faces (“You’re not my real mom”), but Capgras patients do not feel any emotional connection and deem them imposters (“I feel sorry for you, Cindy Lepak”).

This syndrome has long been documented in the neuropsychological literature, and was the basis for Oliver Sacks’ most famous book, The Man Who Mistook His Wife for a Hat.

The book features a host of fascinating neuropsychological case studies, written so the reader really understands the human impact of what has gone wrong with the patient’s brain. The book was first published in 1985 – before the rise of fMRI scans – so while one should not expect the most up-to-date scientific research, the case studies described in the book are still around today, providing insight into how are brains are wired and what can go wrong when things don’t work right.

Sad news in the world of neuroscience . Patient H.M. underwent brain surgery in 1955 to ease seizures he had been having for much of his life. The surgery required removal of part of the hippocampus, which today we know is crucial in the formation of long-term memories.

How do we know this? Because H.M. lost his ability to form new memories. He was the most famous neuropsychological case study in neuroscience, and he passed away on December 2 at the age of 82.

After his surgery, H.M. could not form new memories. Researchers he’d meet every day were completely unknown to him, which suggested to scientists that the hippocampus was necessary for all memory formation.

But then Dr. Brenda Milner tried something out. It was a mirror drawing task. From his obituary in the New York Times:

That began to change in 1962, when Dr. Milner presented a landmark study in which she and H. M. demonstrated that a part of his memory was fully intact. In a series of trials, she had Mr. Molaison try to trace a line between two outlines of a five-point star, one inside the other, while watching his hand and the star in a mirror. The task is difficult for anyone to master at first.

Every time H. M. performed the task, it struck him as an entirely new experience. He had no memory of doing it before. Yet with practice he became proficient. “At one point he said to me, after many of these trials, ‘Huh, this was easier than I thought it would be,’ ” Dr. Milner said.

The fact that H.M. was able to learn a new motor task – and learning requires memory – was revolutionary to the study of memory and the field of neuroscience as a whole. It turns out there’s a conscious memory system where we encode episodic and semantic memories (events and facts, respectively) that rely on the hippocampus, and an unconscious motor memory system that does not require the hippocampus.

Memories are likely stored in a distributed fashion all throughout the brain, but without the hippocampus, no new memories can be created.

In the last years of his life, Mr. Molaison was, as always, open to visits from researchers, and Dr. Corkin said she checked on his health weekly. She also arranged for one last research program. On Tuesday, hours after Mr. Molaison’s death, scientists worked through the night taking exhaustive M.R.I. scans of his brain, data that will help tease apart precisely which areas of his temporal lobes were still intact and which were damaged, and how this pattern related to his memory.

It is sad that he has passed. But he lived to a ripe old age and, while it may not have been a normal life, his contributions to brain science will always be with us.

New York Times Obituary