Manipulating Memory
New Discoveries May Allow Memory to be Alterated and Even Erased
Since the 19th century neuroscientists have viewed memory as a kind of neural architecture, a physical reshaping of the microstructure of the brain. This reshaping of the brain allowed recapitulation of the past to be neurally encoded. New discoveries now indicate that memory may be more like a shifting montage, a narrative spun from bits and pieces of sensory input that is constructed anew whenever recollection takes place.
The Traditional Interpretation of Memory
For more than a century episodic memory (conscious knowledge of a past event or experience) has been defined as an elaborate choreography of neural impulses and over a hundred different proteins.
Traditionally, memory was thought to begin with sensory information coded as electrical pulses zipping along the neural network to the brain. Eventually these electrical signals reach the memory centers of the brain, the almond-sized amygdala, and the banana-shaped hippocampus. Neuroscientists believe that memory forms when neurons in these memory centers are simultaneously activated by glutamate (a chemical neurotransmitter) and an electric pulse.
The glutamate and electrical pulse result in a biochemical waterfall that results in the formation of new synapses and in the adjacent neurons becoming more sensitive to each other. Enacting these changes takes time but after a few hours the process is over and the memory is solidified or said to be “consolidated”.
Traditionally, memory has been regarded as a dynamic process that once established, is almost impossible to reshape quickly if at all.
Karim Nader and a New Understanding of Memory
The science of memory was turned upside down in 1999 by Karim Nader who was a lowly postdoc and not even a full-fledged memory research. Nader put a different spin on a standard experiment in fear research in which rats are trained to associate a tone with an electrical shock to the foot. Rats quickly learn the association and cringe in fear weeks later if they hear the same tone.
Nader trained his rats and they reacted as expected. He later injected them with a protein-synthesis inhibitor, which prohibits new memory from forming. The traditional model of memory held that the chemical should have no effect since the memory of the tone had already been consolidated. However, when Nader sounded the tone again later, the animals did not freeze in fear. He had simply but powerfully demonstrated that reactivating a memory destabilizes it, putting it back into a flexible, susceptible state. Memories can apparently be reconsolidated.
After an initial backlash of skepticism and disbelieve, various groups began testing Nader’s work and expanding it to other species, while other labs began working out the molecular process of reconsolidation molecule by molecule. What has emerged is that many types of memory in many different species reconsolidate and that proteins are actively dismantled when a memory is destabilized, evidence that the old memory is actually changed as it is recalled.
In the July/August 2009 edition of Discover magazine in an article entitled, “Out of the Past,” Joseph LeDoux explains, “Reconsolidation suggests that when you use a memory, the one you had originally is no longer valid or maybe no longer accessible. If you take it to the extreme, your memory is only as good as your last memory. The fewer times you use it, the more pristine it is. The more you use it, the more you change it.”
Has the Era of Memory Treatment Arrived?
Early trials treating post-traumatic stress disorder (PTSD) with the drug propranolol have been encouraging. Symptoms of patients declined by half and stayed that way for up to six months afterward. These patients still remember what happened but the memory is far less disturbing and disruptive of their normal mental functioning.
Researchers must still prove that the improvements will last. If they do, it could offer solid hope to millions of rape victims, car crash survivors, and combat soldiers who are debilitated by PTSD, a powerful disorder from which only a third currently completely recover. Researcher hope that similar treatments can address other psychiatric problems ranging from anxiety and depression to acquired phobias and addiction.
Reconsolidation modifies old memories, but new discoveries point to the possibility of erasing them completely. Research with mice has shown that manipulating specific molecules or injecting inhibitors into different areas of the brain’s memory centers, it is possible to eradicate whole categories of memories. (What some have called “benevolent forgetting.”)
The implications and potential applications of this research are staggering. Neuroscience seems poised on the brink of being able to ease the distress of pathologically deep emotional memories in millions of people.
The Mind Holds Many Mysteries
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