'Eternal Sunshine' is Just Around the Corner

[Q & A] Thanks to advances in neurology, erasing memories is no longer science fiction.

Researchers at the University of California, Los Angeles (UCLA) have announced that they have successfully eliminated, or at least weakened, long-term memories in lab animals, a move that holds promise for research into traumatic memories. We are still decades away from the scenario predicted in the film Eternal Sunshine of the Spotless Mind, in which people purchase the ability to forget unwanted memories. But confronting the issue of memory alteration means answering some tough ethical questions.

THE MARK: What was the purpose of the experiment? What did you hope to achieve?

DAVID GLANZMAN: What we were interested in was the issue of whether or not one could erase long-term memories. There have been several studies that have appeared in the literature lately showing evidence that this can be done in mammals.

The research centred around a protein called kinase, or PKM. The theory is that PKM is what maintains our long-term memories. So the question is, how? What’s going on? That’s very difficult to address in the mammalian brain because it’s so complicated, so we wanted to reduce the problem to the simplest possible level. To do that, we started experiments on the marine snail Aplysia. This species has been a standard model for studying learning and memory for almost 50 years.

The reason we use this snail is that it has a very simple nervous system. It has only 20,000 neurons in its nervous system, compared to approximately a trillion (give or take a hundred billion or so) neurons in the human nervous system.

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If you think about the synaptic complexity of the human brain, it’s stunning. It’s overwhelming. It’s very intimidating. And I’m a reductionist – I like to get things as simple as possible in the hopes we can understand them better.

We studied a very simple form of learning called sensitization. It’s not a type of learning where you form associations among stimuli. A classic example of associative learning is Pavlovian conditioning, where, for instance, a dog learns to associate a ringing bell with food. The experiment that we did focused on a non-associative form of learning where the subject received an arousing stimulus and, as a result, became sensitive to a wide number of sensory stimuli. We essentially created a heightened state of alertness.

What we studied was the snail’s reflex when we tapped its siphon, an organ in the middle of its body. When you touch the siphon, it will contract. The duration of that contraction is a measure of the snail’s arousal, meaning that the longer the reflex lasts, the more sensitized the snail is.

Then we gave the snail sensitization training, which consisted of a series of shocks that were administered to its tail. Then we waited various amounts of time, and we tested the siphon again to measure its reflex duration. What we were looking for was an increase in the duration of the reflex, because that’s an indication of sensitization. The longest we waited was one week, and these snails only live for a year, so a week is essentially a year to them. A lasting reflex was considered long-term memory.

After we tested the snail and confirmed that it remembered the shock, we injected the snail with an inhibitor of the protein PKM. Twenty-four hours later, we tested the siphon reflex again. What we observed was that, after we injected the inhibitor, the reflex reset to its baseline duration. In other words, it was the same as if the electrical shocks had never happened. As far as we could tell, the snail’s memory of the shock was gone.