News Item: Neuroscience

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Immutable Memory:  Research Challenges Long-Held Beliefs

Most people believe in the permanence of long-term memory, especially recollections of significant events, personal or shared—the kind that usually begin with “I remember where I was when…” and include assassinations (Kennedy, King, Lennon), tragic accidents (the space shuttle explosion) and deliberate acts of destruction (the World Trade Center).  Referred to as flashbulb memories, these have always seemed indelibly etched in the brain like a snapshot of a moment in time.

New research suggests otherwise.  In the May 2010 issue of Smithsonian magazine, Greg Miller in his article “Making Memories,” describes the work of Karim Nader who, after discovering that his own memory of September 11, 2001 included television footage from the following day (of the first plane hitting the north tower), began to wonder whether recalling memories altered them.  Support for his questions about the infallibility of flashbulb memories came in a 2003 study that found that 73 percent of the sample group (569 college students) had the same misperception about when they saw the first plane hit.

In the process of experimenting with memory (in rats, and later replicated in other species including humans), Nader found evidence that even a long-term memory could be disrupted by recall.  The more frequently it was remembered and retold, the more vulnerable it was to alteration.

In the brain, communication between neurons (of which there are over 100 billion) is facilitated by neurotransmitters.  These chemicals, produced by brain cells, are released into the synapse, the gap between the neurons, to be picked up by receptors on another neuron.  In the creation of short-term memory, the changes to neurons and their connections are much simpler than for long-term memory, which requires far more neurotransmitter production and the generation of additional receptors.

When a long-term memory is thus encoded, it has been consolidated and long thought to then be permanent.  Nader’s research (along with others’) suggests that reconsolidation of memories can occur under certain circumstances of recall.

Those who struggle to believe their often fragmented and dissociated memories of childhood sexual abuse might take this to mean now they really can’t trust those terrible feelings in their bodies and all their symptoms of Post-traumatic Stress Disorder–those reactivations of the original horrors.  Although some details might have changed in the telling, the essential nature of the original event, that the first plane did crash into the north tower, remained immutable.

In fact, this new conceptualization of memory has led to some hopeful experiments with trauma survivors.  Alain Brunet, a psychologist, had his own close enough experience of a life-threatening situation when a gunman killed 27 people before taking his own life on the campus where Brunet was studying (though he was not in the immediate vicinity).  Inspired by it to study traumatic stress, he has been looking into whether traumatic memories, or at least the distress they cause, can be ameliorated chemically.

Using propranolol, a blood pressure medicine known to produce memory loss by interfering with the production of norepinephrine (a neurotransmitter active in memory consolidation), Brunet had subjects listen to their previously written scripts about incidents (sexual abuse, assaults and car accidents) that occurred ten years before the experiment.  Those who took the medication as compared with those who took a placebo had measurably reduced levels of physiological arousal.

Those subjects who took propranolol and read their scripts weekly for the next six weeks experienced a 50% reduction in their PTSD symptoms.  Long after the effect of the drug wore off, they continued to enjoy a reduction in flashbacks and nightmares.  The memory remained but lost its disruptive impact on their lives.  A traumatic memory seems to have been reconsolidated into an ordinary bad memory offering support for the hypothesis that “recalling memory opens it to manipulation.”

A technique like EMDR that often elicits a powerful reexperiencing of the traumatic event, albeit in a condensed form, might owe some of its effectiveness to memory reconsolidation.  After telling their story, people often come to a different understanding about its meaning.  Sometimes, several weeks later, they will describe how a related negative belief about themselves has been replaced by a positive one.

More research remains to be done, of course, to replicate the propranolol study with other subjects, especially those who suffered family-based trauma during the critical developmental years of childhood.  But it does begins to offer hope for sexual abuse survivors that the very thing they fear about their memories, that they are unreliable and mutable, may end up being the source of relief from their distressing symptoms.