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Would you ever eat a plant whose genes were altered by scientists in a laboratory? You probably
already have, for genetically modified organisms (GMOs), also known as genetically engineered
organisms, are 16 in modern food supplies. The concept underlying genetic modification is not new.
For centuries, farmers have used a method called selective breeding to produce more 17 crops. They do
this by choosing seeds from plants that appear to be particularly 18 to pests and cold or dry weather and
planting those seeds in place of weaker strains. Over time, the desirable strains come to dominate the
genetic 19 of the farmers’ crops. Not everyone is supportive of the technology, however. Critics point
to the fact that GM foods are simply too new to be embraced, 20 that there could exist long-term health
risks that have yet to surface. For instance, consumers with allergies have had adverse reaction to the implanted
genes.
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Post-traumatic stress disorder is a malady of memory. Sufferers are often haunted by recurrent nightmares,
distressing thoughts and flashbacks so intense in color, smell and sound that they feel as if they are reliving the
trauma. But what if these unbearable memories could be selectively erased? Sheena Josselyn, a professor of
physiology and psychology, who studies how the brain encodes, stores and uses information, is intrigued by
the idea and has been investigating how to “silence” memories --make them temporarilyinaccessible-- in mice.
She thinks it’s possible that a variation of this technique could one day help treat post-traumatic stress disorder
in humans.
Studies with mice have found that although their brains contain billions of neurons, only a few are
necessary to form a fearful memory. Researchers working with mice began by teaching them to fear a tone:
when it sounds, they feel a mild shock to their feet (not to hurt them, just to scare them). The next time the
mice hear the tone, they crouch and freeze, signaling fear. The researchers discovered that they could trigger
the memory of that fear even without presenting the tone. They did this by stimulating the small group of nerve
cells holding that memory through a technology called optogenetics. Using the same technology, they found
they could also suppress the fearful memory. With optogenetics, scientists insert proteins into neurons to make
them sensitive to light. Depending on the type of protein and color of light used, these cells can then be
activated or deactivated by shining pulses of the light directly into the brain. If the light activates the cells, the
mice freeze as if they’ve just heard the tone. If the light deactivates the cells, the memory is suppressed. While
optogenetics is an invasive procedure and technologically not feasible with humans, Josselyn hopes that the
general principles learned from these studies could eventually help scientists create new drugs for treating
memory disorders such as post-traumatic stress disorder and Alzheimer’s.