What would your life be like if you could erase certain memories? Maybe you could “forget” about some traumatic event, a deep-seated fear or a relationship gone wrong.

It seems like science fiction, but researchers may be on the verge of making memory erasure a reality.

Fred R. Conrad/The New York Times

Dr. Todd C. Sacktor and his team of scientists from SUNY Downstate Medical Center have been able to show how a single dose of an experimental drug can block the ability of an animal’s brain to hold onto specific types of memories.

To read more about Dr. Sacktor’s work, read Benedict Carey’s article, “Brain Researchers Open Door to Editing Memory.”

Dr. Sacktor’s research raises some interesting questions. How will erasing specific memories affect humans? Will this work lead to a treatment to allow us to retain memory longer?

This week, Dr. Sacktor will answer your questions about memory erasure. Please post your questions and comments below, and check back daily for his responses.

In Response to the Ethical Questions

This strikes me as one of those things that could be extremely dangerous if used improperly. Even ignoring the potential illegal uses, allowing people to erase negative memories is a bad idea.

I’m in general disinclined to promote any kind of ignorance – even if that ignorance would make a person happier. We learn from the past, right? Well, we’re supposed to. And sometimes it is learning from painful memories that we become better people.

The only time I can imagine this being okay is in cases of serious, horrendous trauma – rape victims who now cannot live normal lives, child abuse victims, etc. Only in situations where a person has been completely destroyed from an experience, where there is nothing positive to learn.

But even then, we are denying reality, denying life. And for better or worse, our memories define who we are.

— James W., Washington D.C.

Dr. Sacktor: The purpose of our experiment with ZIP was to try to understand the molecular basis of memory storage, which previously was a complete scientific mystery. The experiments were designed to test the hypothesis that memories are stored by the action of a specific molecule— PKMzeta. You should know that the notion that a specific molecule stores memory goes completely against the grain of how most neuroscientists have thought about long-term memory for decades. Most neuroscientists thought that memories were stored by anatomical changes in the brain, such as new synapses, not by specific molecules. That is why our results showing a very rapid disruption of long-term memories, first published in Science in 2006, were so striking. The results have been confirmed in many labs around the world, with different drugs that inhibit PKMzeta, and for many different forms of long-term memory. Interestingly, ZIP does not affect short-term memory, or once the drug is gone, the formation of new long-term memories in the same brain region.

Elucidating the molecular mechanism of long-term memory may one day be key, I hope, to developing treatments of memory disorders. But don’t forget how long this development from basic science discovery to clinical usefulness takes— decades for even the most important findings, such as germ theory and the structure of DNA.

One important recent publication by my colleagues at SUNY Downstate, Drs. Sue Mirra, John Crary, and Charles Shao, is that PKMzeta is bound up in the neurofibrillary tangles that are found in the brains of patients with Alzheimer’s Disease. This is likely to alter the function of PKMzeta and may contribute to the memory loss characteristic of that disorder.

But I think that the concerns, even the deep unease, that many of the questions voice reflect two striking features of the experiments with ZIP that go to the essence of PKMzeta’s role in memory— features that are also rather surprising to most neuroscientists. These are, first, the rapidity with which long-term memories, three month-old in the rats and presumably decades-old in humans, might be erased. This happens almost immediately with the injection of the drug. Second, is the specificity. As I mentioned, short-term memory, the underlying structure of the brain, and the capacity to form new long-term memories are unaffected.

These two surprising features are because PKMzeta is an enzyme. If you recall from high-school biology, there are two general forms of proteins, structural and enzymatic. Most neuroscientists had assumed that hundreds of structural proteins would be involved in the new synapses thought to store long-term memory. And there would be nothing unique to the structural proteins in the memory-storing synapses, as opposed to those synapses formed in development prior to experience.

But enzymes catalyze very specific chemical reactions and can be rapidly inhibited. That long-term memories are maintained by the constant action of one such enzyme, and thus that memories can be specifically and rapidly erased, was quite a shock.

The Drug’s Uses

What are the primary uses you envision for this drug?

— Rebecka L., New Jersey

Dr. Sacktor: There are a few rare or severe cases of psychiatric or neurological disease in which ZIP might be helpful. I am a neurologist, not a psychiatrist, but I understand that there are clinical situations in which, as a last resort, a procedure known as bilateral cingulotomy can be performed. In this procedure, a small region of the brain is destroyed. I could see that, prior to the destruction of the neural tissue, ZIP might be injected to try to “reset” the synapses in that region. The drug diffuses around 1-2 mm from an injection site in the brain, so the region affected would be restricted.

For more general application, we have to develop an activity-dependent form of ZIP, i.e., a drug that becomes active only when the neurons are firing intensely, as when a memory is recalled. This might allow a specific, recalled long-term memory to be erased, rather than all long-term memories. I should add that there is a entire subfield of memory research studying the role of what is called “reconsolidation blockade” that aims at essentially the same thing. This work is very exciting and has been lead by my colleagues Karim Nader, Joseph LeDoux, Susan Sara, Cristina Alberini, Yadin Dudai, and others. You may have heard about the studies with propranolol on trying to reduce the emotional component of post-traumatic stress memories. How this reconsolidation work fits in with PKMzeta is actively being explored.

Developing memory enhancers that convert short- into long-term memories by increasing PKMzeta in the brain is also a possibility. This has even been done experimentally in the fruit fly by my colleagues, Jerry Yin and Eric Drier, when at the Cold Spring Harbor Laboratories, and now at the University of Wisconsin, Madison.

Is Memory Loss Permanent?

Has the research been ongoing long enough to answer the question of permanency? Is the memory erased forever? And, further, how does the nature of the drug and its effect (physically and chemically) on the brain lead to greater understanding of how memory works. Will dementia figure in the coming research?

— William H. Porter

Dr. Sacktor: Three month-old memories in the rat have been erased. Although I don’t really buy the analogy, this is equivalent to a 10 year-old memory for a human (rats live around 2 years). I do not see any compelling reason why a three month-old memory would have a biologically different basis than a decades-old memory, but you never know.

We, as well as other researchers, have done extensive experiments to try to see if, once disrupted by ZIP, a memory ever comes back. We waited weeks, we gave reminders, but the memory never seemed to return. Remarkably, giving the drug right before or even during the training had no effect on long-term memory formation tested a few days later. The drug has a pure “retrograde” effect. That’s why it’s so different from clinical cases of amnesia due to brain injuries or dementias like Alzheimer’s, which affect both formation of new memories and recall of old. Our experimental result also suggests that the PKMzeta is not made immediately during learning, but after a few hours, and that the drug itself only lasts a few hours.

Please check my other responses for answers to your other questions. Thanks.