Are scientists on the brink of learning how to erase memories?
The great dread of our age is the insidious onset of Alzheimer’s disease, the inexorable loss of the very memories that constitute our individuality, our personhood. Big pharmaceutical companies are investing massively in drugs which might retard or even prevent the decline and preserve the failing memory. Yet, suppose our memories are painful, bringing back painful experiences. Might it be possible to erase them, wipe them out as cleanly as pressing the delete button on a computer?
Memories fascinate scientists, perhaps because they are created in such a complicated fashion. Our senses are continually bombarded with information, some novel, some a repeat of previous experience. Much is ignored, some is remembered for a few minutes only (short-term memory), and a proportion of that is retained more permanently (long-term memory). Within the brain, short-term memories are “held’’ in the form of transient increases in neurotransmission between nerve cells, notably in a region known as the hippocampus. But translating short - into longer-term memory involves more permanent structural changes in the connections (synapses) between the nerve cells. This process involves a cascade of biochemical mechanisms, triggered by the initial increases in neurotransmission resulting eventually in the creation of new proteins. These move to the synapse, modifying its structure.
Because a sequence of biochemical steps is required to reshape the synapses in the hours after an important event or experience, it is possible to use drugs or inhibitors to disrupt the process. Indeed it is through the use of such specific drugs that many of the steps have been explained.
Say you find out your partner is having an affair. Would it be possible to excise the moment of discovery from your brain? Disrupting neurotransmission in the minutes after the experience, or blocking protein synthesis in the hours that follow does prevent long-term memory being formed, and the result is amnesia of that event. However, blocking protein synthesis outside this critical period leaves memory unimpaired. So the conventional wisdom, at least since the 1960s, has been that once a memory is “fixed’’ bio-chemically, it is permanent and cannot be erased.
There have always been some anomalies that have sat uncomfortably with this assumption — for instance, memories don’t stay in the hippocampus; it seems that after some days or weeks they are transferred to the cerebral cortex. But the community of memory researchers has mostly tried to ignore such inconvenient data.
Four years ago, Karim Nader and his colleagues in New York showed that if an animal was taught a particular task, and then days later was reminded of it by being put in the same context, the memory became labile (prone to change) once more — that means it could be disrupted by protein synthesis inhibitors. It was as if the reminder not only reactivated the old memory, but resulted in an entirely new memory being formed on top of it. Of course, we can intuitively recognise this; when we recall a past event, we are not recalling the event per se, but our memory of it from the last time we recalled it. This is why our autobiographical memories are being reshaped as we go through life.
It seems these days that in the immediate aftermath of any horrific murder or other disaster, grief counsellors are blue-lighted in to treat survivors, relatives and shocked bystanders. Soldiers returning from battle, police and emergency workers, even those recovering from a messy divorce, are being diagnosed with PTSD, whose symptoms are described as recurrent and intrusive distressing recollections of the event, including images, thoughts, perceptions or dreams, acting or feeling as if the traumatic event were recurring. So might it not prove possible to erase the unwanted memory? All
that would be necessary, if the animal experiments are right, would be to re-evoke it - perhaps by revisiting the scene - and then inject some biochemical blocker and it would be gone for good.
So enthusiastic have some advocates become that even the US President’s Bioethics Council has been obliged to consider the possibility.
The trouble is that any such treatment is likely to be pretty toxic and the side-effects more serious than the PTSD they are trying to cure. There are several US companies in the memory drug business, mainly searching for agents that will enhance memory, but their publicists have already been quick to point out that erasure is the flip side of enhancement, and that if they can achieve the one, a quick toss of the pharmacological coin will come up with its opposite.
Leaving the ethical issues to one side, a non-toxic drug is unlikely to have the desired effect. The animal experiments are run in controlled conditions in which both the initial learning experience and its recall are precisely managed by the experimenter. Just how to reactivate the terrors of the multiple experiences of the survivors of a train crash, still less the richness, pain and pleasure of a love affair gone awry beggars imagination. And because the memories concerned are vastly more complex than those involved in a rat anticipating an electric shock, they are going to engage many more neural processes.
To achieve the vestal virgin’s happily spotless mind will take more than pharmacology. It may even need such old-fashioned techniques as talking through the problem. Some years ago an experiment showed that for mildly depressed people psychotherapy could achieve the same effects on the body’s biochemistry as could taking a standard anti-depressant drug. The brain/mind is after all a profoundly social organ, and memories are more than mere molecules.