As LaBar and Cabeza learn more about the amygdala and its associated circuitry, they are coming to appreciate the subtle complexity of the modest little structure. "When we started this work, it was thought that the amygdala was a specialized fear modulator," says LaBar. "We do still believe that, but we're also finding that it influences maternal and sexual behaviors. We know very little about its role in such reward-based behaviors." Nor, says LaBar, do researchers understand how the amygdala might affect unconscious learning, such as skills or habits.
An especially fascinating question arising from studies of emotional memory is whether scientists could ever invent a "magical memory pill" to alleviate PTSD or traumatic memories. Some preliminary clinical studies around the world have raised the possibility. A handful of subjects in the U.S. and France are participating in studies in which they were given the drug propranolol immediately after a terrorizing experience such as an attempted rape. The drug blocks the action of stress hormones, including adrenalin, that activate the amygdala to imprint emotion-charged memories on the brain.
So far, the studies have only given early hints that the drugs might reduce the disturbing intensity of such memories, and research is continuing. Says LaBar, "While there could be designer drugs to either enhance or suppress emotional memories, there are huge problems in terms of ethics and specificity." He says the new appreciation of the amygdala's complex role in making memories means that "designing drugs to target specific emotions within the amygdala is going to be a major challenge." And how about the likelihood of a drug or treatment to erase specific memories, as depicted in the movie Eternal Sunshine of the Spotless Mind, in which a woman deletes memories of her ex-boyfriend? Never going to happen, assert the researchers: Recalling even the most specific memories involves the entire landscape of the brain.
Nevertheless, they say, future studies will likely provide additional insights into the neural circuitry of memory, including emotional memory--revealing more, for example, about how genes control the formation of such neural circuitry, as well as its function in influencing behavior. A prime example of the far-reaching implications of those studies was a discovery--reported in the December 2004 issue of Neuron by Duke cell biologist Marc Caron and his colleagues--of the first genetic defect specifically linked to depression and resistance to antidepressive drugs.
Cabeza emphasizes that among the most important advances required to understand the brain will be correcting the mental biases of brain scientists themselves. "We need to break free from the taxonomy of cognitive processes we inherited from the last century," he says. "We've all been trained to think of cognitive abilities in terms of discrete functions such as memory, attention, perception, imagery, and so forth. However, we now realize that the same brain regions are activated by a variety of functions. So, it's a bit funny that when you read a scientific paper, if the paper is about memory, the authors say activity in a given region is due to memory. And if you read a paper about language, the authors say the same region is involved in language. But we're now at a point where it's obvious we cannot keep attributing a brain region to our favorite process."
"We have to find new ways to explain activation of regions that can accommodate many processes and get beyond this rigid classification," says Cabeza. "We need to build bridges between the two different worlds of studies of cognition--the psychological tradition and the neuroanatomical tradition. It's a big challenge, but it offers great promise for understanding the brain and its disorders."
The impact of deeper knowledge of emotional processing will be profound. Understanding our own neural demons might mean, ironically, not only trying to vanquish them, but also, ultimately, embracing them. After all, we are the culmination of all our memories, those of rampaging roosters--and of tender kisses.
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Duke Magazine-Deep in the Heart of Memory by Dennis Meredith-May/June 2005
June 1, 2005