What is the sound of one cockroach leg flapping? Students in the second trimester elective Neuroscience recently found out—and were startled by what they heard.
The lab activity: gently stroking a freshly severed cockroach leg and listening to the resulting electrical signals amplified to the point of audibility. “It sounds like fireworks,” said one student while engaging in the lab. Other students compared the sound to a crackling fire, to radio static, or to the ocean.
“What are you hearing?” asked science faculty member Sequoyah Reynoso, who teaches the class. The answer was clear to the students, who had been learning how electrical impulses in the brain and nervous system control the movements of roaches, humans, and most creatures in between: action potentials. An action potential is another term for the nerve impulse that carries information to and from the brain, ultimately resulting in sensation or movement.
Reynoso had ordered six large roaches, along with the necessary equipment for housing them and conducting the lab, from a company called Backyard Brains, which creates educational science products. “When I was in grad school at UC San Diego,” says Reynoso, who holds a PhD in neuroscience, “we had an outreach program where we used the same equipment to spread knowledge of the secret world of neurons.” Reynoso recalled the “enthralling lesson” when he became a teacher, and this year he’s incorporating it into his lesson plan for the first time.
The roaches arrived in early December. “The box was delivered to Blackwell House,” Reynoso recounts, “and Lindsey Robb, who works in that building, emailed me to say, ‘There’s a box here that says it contains live insects!’ Lindsey seemed a little alarmed when I came to pick them up.” Fortunately, roaches are famously low maintenance, and Reynoso kept them alive over winter break with no trouble. “They can live entirely on lettuce,” he notes, “and can go two weeks without eating anything.” And though some of those roaches would have a leg removed in the interest of science, it’s a renewable resource: roach legs, says Reynoso, will regrow in about 120 days.
In the classroom, where the roaches lounged in a vivarium on a bed of spinach from Kraft Dining Hall while awaiting their turn under the knife (actually, scissors), students broke into small groups of two or three to take a turn placing the leg on a “spiker box” that allowed them to hear the nerve impulses that fire up when the leg is stroked. The first group worked with a leg that had been amputated earlier in the day; the signals it emitted were audible but muted, as the neurons gradually stopped firing.
Then it was time to procure a fresh leg. Gregg Dennison ’21 stepped into the role of roach surgeon, first immersing the roach in ice water to anesthetize it. Then he took up the scissors, with Reynoso instructing him to cut at the coxa, the cockroach equivalent of the upper thigh. The amputation completed, students listened to the new leg as it responded to stroking. The sound was notably louder. Students also observed that, as one put it, “The harder you push, the louder it sounds.”
Another phase of the experiment would involve making the roach’s leg move in time to music played through an attached MP3 player; later in the term, there was the prospect of implanting a neural prosthesis into the roach’s antennae that would make it possible to influence the insect’s movement with a swipe on a phone screen. Such actions, notes Reynoso, raise ethical questions as well as scientific ones, and those concerns have been part of the discussion throughout the semester. “Research on live animals should be conducted with the utmost respect; the scientist should always strive to reduce or eliminate any negative effects as much as possible,” he said.
Once the experiment was concluded, students spread out to write up their lab reports. “Mr. Reynoso, how do you feel about exclamation points in a lab?” asked one. “I love exclamation points!” Reynoso shot back.
Reynoso encouraged students to find their way to the answers by referring to what they had just encountered during the lab activity, asking questions about how action potentials work and tying that to the broader themes of the course. Earlier, he’d speculated that some students might be “too squeamish” to enjoy the lab, but in the moment, most seemed to share one student’s assessment: “This,” she said, “was so cool.”