One area of brain science that has drawn intense interest in recent years is the study of what psychologists call reconsolidation—a ponderous technical term that, once translated, means giving yourself a second chance.
Memories of our daily experience are formed, often during sleep, by inscribing—or “consolidating”—a record of what happened into neural tissue. Joy at the birth of a child or terror in response to a violent personal assault.
A bad memory, once fixed, may replay again and again, turning toxic and all-consuming. For the traumatized, the desire to forget becomes an impossible dream.
Reconsolidation allows for a do-over by drawing attention to the emotional and factual content of traumatic experience. In the safety of a therapist’s office, the patient lets demons return and then the goal is to reshape karma to form a new more benign memory. The details remain the same, but the power of the old terror to overwhelm and induce psychic paralysis begins to subside. The clinician would say that the memory has undergone a change in “valence”—from negative to neutral and detached.
The trick to undertaking successful reconsolidation requires revival of these memories without provoking panic and chaos that can only makes things worse. Talk therapies and psycho-pharm may not be enough. One new idea just starting to be explored is the toning down of memories while a patient is fast asleep
At the Society for Neuroscience meeting last week, a French research group offered a proposal for how to move forward. Karim Benchenane of the Centre National de la Recherche Scientifique in Paris told a press gathering that his team had inserted into a mouse’s brain an artificial memory of sorts. The implanted memory was not the image, smell or taste of delectable Swiss cheese. Accomplishing that feat remains a challenge far beyond the capabilities of current technology. Instead, while the mouse slept, the CNRS researchers created a new emotional memory in the rodent’s brain, a pleasant feeling about a particular location the animal had trod over the day before inside its lab enclosure.
The team used an electronic tool, a brain-machine interface, to record place cells that fired as the animal ran through a track-like enclosure. Place cells became world famous in October when John O’Keefe of University of College, London received the 2014 Nobel Prize for Physiology or Medicine for his discovery of these neurons in the hippocampus, where a particular place cell fires to signal a given spatial coordinate in a mental map of its environment.
The CNRS researchers knew that the hippocampus replays recent activities during sleep—in this case, the mouse’s meanderings through the enclosure. So the team recorded the firing of cells in the hippocampus as the mouse slept. Each time a particular place cell fired that corresponded to a given spot in the enclosure, researchers electrically stimulated a reward area, the medial forebrain bundle. In neuro-speak, they turned up the positive valence of that particular place cell. The newly formed emotional memory conveyed to the animal that this was a charmed place. And, sure enough, when the mouse awoke, it went right to the spot that it now fondly remembered.
So what does this have to do with trauma and terror? The same general process might be used one day to treat humans with PTSD. Sophisticated brain scans have already recorded a sketchy movie of a person’s dreams. Spatial memories are fundamental building blocks of any dream, whether in human or mouse. If the recording techniques could be further refined, researchers might be able to observe when a traumatic experience occurs in humans during dreaming. They could then deduce relevant place cells that fired at just that time. Finally, the medial forebrain bundle or another reward center could be stimulated to neutralize the fear associated with the initial stressful experience that produced the nightmare.
If taken as far as it it could go, this type of technology holds some disturbing implications. Inducing positive valence in solidiers watching a film of a bloody battle scene sounds to remove past or future fears like a distinctly bad idea. But before bringing in the bioethicists, Benchenane, who also holds an affiliation with the Ecole Supérieure de Physique et de Chimie Industrielles in Paris, wants to work out a few more details. He would like to know what happens, for instance, when you create a new artificial memory with positive valence and place it alongside an existing traumatic memory. Do good and bad recollections coexist side by side and what does that do to a rodent’s mental state?
There is still a long way to go before neuroscientists build an electronic dreammaker.