Unlocking the Emotional Brain - Page 3


By 2004, neuroscientists had identified the key sequence of experiences that gets the brain to unlock a long-held emotional learning. Especially illuminating were findings from experiments done first at the Neuroscience of Memory Laboratory of the University of Buenos Aires by Maria Eugenia Pereira, Hector Maldonado, and Luis Maria Perez-Cuesta, and then replicated by a team led by Akinobu Suzuki of the Applied Bioscience Faculty of the Tokyo University of Agriculture. In these experiments, the neuroscientists presented a trigger to an animal, such as a red light that previously always glowed just before a foul odor was administered. Just seeing the red light activated the implicit schema—red light equals bad smell—which caused the animal to expect and try to avoid the odor.

After a time delay, they turned off the red light—the trigger—without ever introducing the odor. Turning off the light didn't merely end the animal's expectation of odor, it created a sharp mismatch between what it expected according to the reactivated schema (the odor) and what it actually experienced (no odor). In that experiential moment of mismatch, the synapses of the schema's neural circuit molecularly unlocked, like an unlatching of train cars still sitting in place. The synapses had become "labile," meaning the neural circuit was now changeable, but not yet changed. During the brief window of lability, the schema can be modified or erased permanently.

In these and other studies, to get erasure, neuroscientists administered a chemical agent known to prevent synapses from forming functional circuits. When the circuit's reconsolidation was chemically blocked in that way, the circuit was erased. Whether chemical erasure can ever be made safe for human use is a complex matter, both technically and ethically. But what the experiment showed was that once the schema was erased, subsequent exposure to the red light got no response, permanently.

Subsequent studies confirmed these surprising results. In an April 2007 review in Nature Neuroscience, erasure was successful in 24 of 43 studies—slightly over half. The authors, Yale neuroscientists Natalie Tronson and Jane Taylor, suggest that all of the studies might have yielded successful erasure if the other 19 studies had set up the correct conditions for reconsolidation, and that exploring this possibility might better define what the conditions for reconsolidation are.

All of these erasure findings were on animals, but neuroscientists have little doubt about the carryover to the human brain. From fruit flies to Homo sapiens, the amazing sameness of neural mechanisms is well established, and, recently, the unlocking and relocking of memory circuits has been detected in humans. In fact, a study of infants at Rutgers University by Lissa Galluccio, published in 2005, found that erasure of an implicit memory could be achieved experientially, not chemically—a promising outcome.

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