WE Remember, Because HM Forgot

Henry Gustav Molaison

So many big moments in the history of neuroscience are the products of efforts to understand or treat epilepsy. Look for instance at this fine recent story by Mo Costandi in the Guardian memorializing one of the most important figures in the field, a man who for decades was known simply as HM. Henry Molaison (whose full name was only released upon his death two years ago) had been dogged by seizures since childhood and was so desperate to shake them that, in 1953, he agreed to have his hippocampus removed. His surgeon knew HM's seizures were originating there, but no one knew what the side effects would be. The surgery had its intended effect; his seizures were reduced from dozens a year to about two. But in exchange for that gain, he lost the ability to make new memories, a condition known as severe anterograde amnesia.

The main character in Memento, the excellent movie about an amnesiac driven to keep progressing into the future by preserving his past with Post-Its, annotated Polaroids, and tattoos, was purportedly modeled after Molaison.

Before Molaison, most neuroscientists believed memory to be distributed all through the brain.  The first paper about the case, published by Molaison's  surgeon, William Beecher Scoville, and neuroscientist Brenda Milner (both at the Montreal Neurological Institute) showed that though even without his hippocampus Molaison could still retain small amounts of information for short periods of time, he couldn't store them anywhere before they were supplanted by new ones. This suggested, for the first time, that memory has distinct long- and short-term components. Memory research has never been the same, and today no one doubts the central role of that weird little seahorse-shaped part of the limbic system known as the hippocampus in creating and quickening new memories; it is now arguably the most intensively studied part of the brain.

Molaison died two years ago, at 82, but his brain (still being studied at the Brain Observatory UC San Diego) is still revealing secrets about the nature of memory and what makes it work--and cease working.

It's hard to say where memory research would be today if it weren't for Molaison and his epilepsy; possibly decades behind where it is now.  Let's not forget him...or the many other courageous and generous patients with epilepsy who shed so much light on this field.

What's That Movie Called?: Memory in Film

There’s a movie I can never remember the name of. It’s about a man who has no short-term memory. It begins with the letter “M,” but it isn’t a person’s name. "Manifest?" No, it has something to do with memory. I know it! I know it! I’ve seen the film twice and it is excellent, a tour de force, but I can’t remember the name!  "Manifest!" No! Damn!

In this movie—it’s on the tip of my tongue--Guy Pearce plays Leonard, who suffers from anterograde amnesia, which is a loss of the ability to create new memories. Memories from before the trauma that caused the amnesia remain intact and accessible. New memories never make it from the hippocampus, where memories first form, to wherever they’d be stored for long-term retrieval. Leonard earned his amnesia by interrupting two men who were attacking his wife; he gets a hard whack on the head. He can recall events from before the accident, but nothing new sticks.

To compensate, Leonard surrounds himself with mnemonic aids, fills his pockets with annotated Polaroid photographs and Post-Its. His most striking device, though, for those bits he really can't afford to forget, is the drawing of rich-text tattoos all over his body.
It’s a murder mystery, told in reverse, that is stunningly, delightfully, reelingly complex. The plot gets less and less clear the more you learn. Until the end, when everything becomes clear...or at least coherent.

Leonard's memory loss is so poignant, maybe, because it's a caricature of the normal human condition. Our experience leaks through the sieves of our memories,  while only a few rare bits make their way to long-term storage. It's hard not to mourn the extravagant waste of that. But it's also the secret to our sanity and the coherence of our lives; the trick to memory is not just knowing what to preserve, it's the ability to drop whatever dilutes and confuses the story without adding value. And as this movie reveals, the forces that determine what we preserve, and the stories we weave with that material, are not always conscious. Or honest. You can play the film instantly on Netflix and if you’re interested in memory you should.

Of course, there’s an epilepsy angle: one of the most common causes of anterograde amnesia is temporal lobe surgery, usually for epilepsy with a focus in the medial temporal lobe. Also, some kinds of temporal lobe seizures themselves mess with the same brain areas, and can cause temporary bouts of anterograde amnesia. The hippocampus, and all of the stuff surrounding it, regulates the acquisition of short-term memory. Damaging it is like firing the librarian who files the books to the shelves. New volumes keep coming in, and you can see them as they do, but they quickly get lost in the pile and are impossible track, let alone read.

Memento! Of course, the movie is called Memento!

My next blog should be about TOT (tip of the tongue), a bonafide neurological phenomenon. It's also called Presque vu, from the French for “almost seen.” You know the feeling, it’s when a word or name you know well is right there, but not accessible. "Memento" is one that I, for some reason, have a hell of a time accessing. William James described TOT, back in 1890, as “a (memory) gap that is intensely active.” It feels like there’s a repulsive force involved, not just a lack of connection.  That’s why we sometimes need to Jerry-rig our own memories, to overwhelm those "intensely active" gaps. Maybe I should have “Memento” tattood on my thumb. What do you think?