Friday, April 22, 2016

Henry Molaison and his “Permanent present tense”

Meditators do years of practice so that they can live in the present moment. Henry Molaison for most of his adult life had no choice but to live in the present moment. As a person with amnesia since the age of 27, he had no concept of yesterday and tomorrow. When asked, “What will you do tomorrow?” Henry answered, “Whatever is beneficial.” Henry Molaison also known as H.M. through the psychology textbooks and literature is the most studied subject in the history of neuroscience. The book “Permanent present tense” by Prof. Suzanne Corkin of MIT whose lab studied Henry as a subject for over 40 years, captures the story of both Henry as well as the neuroscience of memory.

I first heard of Henry when I watched the second episode of the six part PBS documentary “The brain with David Eagleman” titled “What makes me?” Henry underwent a brain surgery at the age of 27 in 1953 as the last option for his sever epilepsy. The surgeon removed both the sides of his hippocampus – a 3 cm component buried deep inside each side of our brain. Henry recovered from his epilepsy but the surgery took away his ability to form long term memories. If you walked out of a meeting with Henry and returned after a few minutes, Henry would greet you as though he is meeting you for the first time. In fact, when researcher Morris left and re-entered the room after some time, Henry said after greeting him, “There’s an empty chair. You go sit there.” That was, of course, the same chair Morris was sitting before he left the room. While being amnesiac Henry was intelligent, articulate and perceptive.

Did Henry lose all types of long term memory? No. One of the breakthrough results in understanding long term memory happened when researcher Brenda Milner administered the star tracing experiment with Henry as the subject in 1963. The procedure involved tracing a five point star by looking in the mirror and it was done multiple times over three consecutive days. The task was challenging and involved learning a new motor-skill allowing a reversed visual image to guide the movement of the hand. Every time Henry began the experiment he had no memory of the previous try. However, Henry’s error rate kept dropping as the first day progressed. His error rate at the start of day-2 was similar to where he left off on day-1. On the third day, He performed nearly perfectly, his pencil rarely crossing the boundary. On day-3, after one of the trials Henry observed, “Well, this is strange. I thought that that would be difficult, but it seems as though I’ve done it quite well”. This showed that Henry hadn’t lost all types of long term memory formation. He had lost what we call episodic memory (What did I eat for breakfast this morning? And with whom?) and semantic memory (What are the names of my friends? Knowledge of people, places). However, he had retained procedural memory (How to use a walker, remote, joystick etc.) When Henry passed away in 2008, he had been using a walker for over a decade.

Henry was mostly an “amiable, smiling” man, but did he ever get upset? Occasionally, he did get frustrated, sad, aggressive or uneasy but these negative emotions would typically dissipate as soon as he was distracted. There were no new associations getting formed that were binding the incident or person or object to an emotion. Perhaps there lies a clue to human suffering – storing a connection between an external situation or person with a negative emotion in the long term memory.  We can carry anger or guilt for years and retrieve it as soon as the link is activated. Henry’s story prompts us to pay attention as we form and retrieve these links every day.

After Henry passed away his brain was scanned in an MRI machine for nine hours. Later it was cut into 2401 ultrathin slices from front to back. These slices have been digitized and assembled into a three-dimensional image that scientists and the public will be eventually view on the web. I liked the way Prof. Corkin concludes the book – Although he lived his own life in the present tense, Henry had a permanent impact on the science of memory, and on the thousands of patients who have benefited from his contributions.

I recommend the book to anyone wanting to understand the development of neuroscience of memory, how experiments are designed in neuropsychology and the role memory plays in our day-to-day life as well as building a narrative called “I”.

Book cover, Henry’s picture are from the book “Permanent present tense”.
Mirror tracing image is from Psychology textbook by Peter Gray.

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