Manipulating Memory

By Emily Singer
MIT Technology Review, May/June 2009

Edited by Andy Ross

Calling a memory to mind makes it vulnerable to alteration. The right drug given at the right time can make parts of it disappear altogether. In a process called memory reconsolidation, after someone calls up a memory, it has to be stored in the brain anew. During this process, the memory is in a changeable state.

Alain Brunet, a clinical psychologist at McGill University and the Douglas Institute in Montreal, is studying reconsolidation in humans. In his trials, he administers propranolol, which blocks the action of epinephrine both in the peripheral nervous system and in the amygdala, a part of the brain that plays a crucial role in storing the emotional components of memory.

A memory is thought to be stored in the brain by a specific circuit of nerve cells linked by synapses. New memories are formed when synapses form or existing synapses grow stronger. It takes time for these memories to become permanent, in a process called consolidation. Very new memories can easily be kept out of permanent storage. But a day or so after a new memory is created, it becomes consolidated.

In 1999, researchers in neuroscientist Joseph LeDoux's lab at New York University found that injecting a drug that blocks protein synthesis directly into part of the brain disrupted consolidation of new memories. Researchers proposed that when the right proteins aren't produced, nerve cells can't make the connections that underlie memory formation at a cellular level.

In 2000, Karim Nader, then a postdoctoral researcher in LeDoux's lab, showed that the same drug treatment could also erase long-term memories that had recently been recalled. Nader proposed that recalling a memory causes the synapses encoding that memory to weaken or even to come apart. The molecular structure of the memory is then reconsolidated to make it stable once again.

Evidence for the theory of reconsolidation is piling up. For example, blocking the molecules involved in protein degradation makes animals forget a memory after it's been recalled. The finding suggests that reconsolidation is why such memories don't normally vanish. They also imply that our memories are vulnerable to alteration.

Jonathan Lee, a neuroscientist at the University of Birmingham in the United Kingdom, trained rats to fear a certain chamber by shocking them when they entered it. More training strengthened the association. Then Lee blocked a protein required for the consolidation of new memories. In a second set of animals, he instead blocked a gene that is critical to reconsolidation. He found that blocking consolidation did not interfere with the strengthening of the memory, while blocking reconsolidation did. So reconsolidation, not consolidation, is important in strengthening memories.

Brunet and his colleague Roger Pitman, a psychiatrist at Harvard Medical School, have shown that military patients given propranolol in the emergency room are less likely to develop post-traumatic stress disorder. But the time window for treatment is limited. Even treating people four to six hours after the trauma may be too late.

Blocking the reconsolidation of traumatic memories should help make these memories less troubling. In a pilot study, administration of propranolol to patients seemed to soothe the anxiety provoked by traumatic memories. Preliminary findings from a larger study show a big improvement among those taking the drug.
 

AR  Intriguing research — and worth reconsolidating in case one gets traumatized.