Harvard Medical School
Dr. Wilson is also a professor of neurobiology at Harvard Medical School. She was an HHMI early career scientist from 2009 to 2013.
Sensory Processing in Small Circuits
The notes of a Beethoven symphony may shake your eardrums, but you can't tell the trumpets from the violins until these vibrations are transmuted into a format your brain can understand. Rachel Wilson studies how the brain makes such transformations. She's learning how circuits of neurons encode impulses from sensory organs like the ears or the nose so an animal can obtain the information it needs to survive—or to enjoy a piece of music.
To Wilson, the brain has always been "the most interesting thing on the planet." But as an undergraduate at Harvard University, she wasn't sure how to turn her fascination into a career. "I thought you had to be a neurologist," an ambition she abandoned after shadowing a neurologist and noticing how few treatments were available for patients, she says. Eventually, after a few trips across town to the medical school library, she says, "I learned that you could study the brain as a research scientist."
Once she was on the right track, in graduate school at the University of California, San Francisco, she quickly made an impression in the field. The prevailing view was that traffic in synapses—the communication channels between neurons—travels in one direction: the neurotransmitters that carry messages wend from the transmitting neuron to the receiving one. Wilson and her graduate adviser, Roger Nicoll, showed otherwise. "What we figured out was probably the clearest example of the violation of that principle," she says. In 2001 they revealed that, like cars driving the wrong direction down a one-way street, certain molecules called cannabinoids—relatives of the compounds in marijuana—travel backward in synapses. By going against the flow, cannabinoids deliver feedback to transmitting neurons and thus might enable synapses to fine-tune their activity.
Wilson also made an impact during her postdoctoral research in the lab of Gilles Laurent at the California Institute of Technology. To decipher how neural circuits function, researchers often use electrodes to record the activity of individual neurons in vivo. Wilson, along with Laurent and fellow postdoc Glenn Turner, realized how to extend this approach to the brains of fruit flies so they could capitalize on the genetic tools available in flies. There had previously been some steps in this direction: other neuroscientists had already succeeded in recording from neurons in fruit fly larvae and in adult brains removed from the head.
Because the fly brain is smaller than a poppy seed, it was a technical achievement for Wilson and colleagues to make recordings in living adult flies from individual neurons. A little improvisation was important for their success. To target a neuron, the researchers would cut an opening in the top of an anesthetized fly's head and guide the electrodes into position while looking through a microscope. A light shining through the translucent bottom of the fly's head provided the necessary illumination for the procedure. But to access this translucent area, the researchers had to move aside the insect's snorkel-like proboscis. The best tool for that, it turned out, was a snippet of human hair. After trying several options, Wilson found that the best hair for the job came from her husband's head. "It's very straight and uniform," she says, perfect for nudging the proboscis out of the way. Wilson brought a bag of her husband's hair into the lab, and it became a hot commodity, she recalls.
Since starting her own lab at Harvard Medical School in 2004, Wilson has been investigating how neural circuits in the fly's brain process odors so the animal can make sense of them. The scent of a banana, for instance, stimulates a fruit fly's olfactory receptors to fire in a specific pattern, which then induces a distinct pattern of activity in other neurons. By recording from different cells in the fly brain, "we trace how signals change as they move from one neuron to the next," says Wilson, who became an HHMI early career scientist since 2009. Wilson has recently also been investigating how sounds are processed by the fly brain. Male flies sing a courtship song to females, so hearing is important to a fly's ability to find a good mate.
Wilson's research has revealed that the olfactory and visual systems overlap in how they adjust gain, the strength of the response to stimulation, relying on a similar type of transformation called divisive normalization. "That's a fundamental similarity in the 'software' that's running on these systems," Wilson says. Her lab is now looking for core similarities among these systems and the fly's sense of hearing. She's asking, for example, how neurons render different features of a sound, such as the power of the trumpets or the clear tone of the oboes in Beethoven's Fifth.