A low buzzing erupts into a loud static noise that fills the Duke lecture hall.

University of Michigan neuroscientist Gregory Gage describes the noise as the “most beautiful sound in the world.” It’s not the sound itself that evokes such fascination, but the source: this is the sound of electrical signals coming from neurons inside an amputated cockroach leg. 

With a background in electrical engineering, Gage credits this sound as the moment that got him interested in neuroscience. He now travels the country as an educator to bring his experiments to the public and encourage interest in neuroscience. His organization, Backyard Brains aims to bring research outside of the lab, and make it accessible to children and students everywhere. On Feb. 2, he presented the Gastronauts Seminar in the Nanaline Duke Building.

His first on-stage experiment aims to understand how information is encoded inside neurons, specifically the neurons located inside the barbs on cockroach legs. In order to record the signals without the roach running off, the first step is to amputate the cockroach leg. For all those worried for the well-being of the roach, rest assured that it was first “anesthetized” in a bath of ice water. (It’s still up for debate if cockroaches can truly feel pain, but Gage likes to err on the side of caution). Importantly, cockroaches also have the ability to regenerate limbs. In about five weeks a new leg will start to grow to replace the one that has been lost, and the entire regrowth will be completed in about 3 to 5 months. 

Underneath each hair on the leg of a cockroach, there is a neuron that detects stimuli and sends electrical impulses up to the brain.

The second step is to place electrode pins through the legs. Two pins are required so that the current will flow through the leg. One pin is located where there are very few neurons, serving as the ‘ground.” This experiment will measure the difference between the two pins, multiplied by the gain provided by an amplifier which makes the signal easier to see and hear. 

Turning up a volume knob on the amplifier, a low static buzzing becomes audible throughout the lecture hall. As Gage is the first to admit, “it doesn’t sound like much” at first. There are a few possibilities: maybe there is no neuron activity, maybe the leg is dead, or maybe it’s just not stimulated. The leg barbs contain stretch receptors: important sensory structures that play critical roles in detecting vibration, pressure, and touch.

These receptors are a type of ion channel, which are proteins located in the plasma membrane of cells that form a passageway through the membrane. They have the ability to open and close in response to chemical or mechanical signals. Stretch-activated ion channels respond to membrane deformation. When compressed, they allow ions to flow through, creating an immediate change in the transmembrane gradient and allowing for a rapid signaling response. The flow of ions is a flow of charge, and constitutes an electric current.

The opening and closing of ion channels underlie all electrical signaling of nerves and muscles. Why has the nervous system evolved to use electricity (as opposed to a chemical diffusion process)? Because it’s fast. And often our lives (or that of a cockroach) depend on responding quickly.

At the direction of Gage, a volunteer lightly brushes the cockroach leg. Suddenly, a change in the noise: short static bursts in volume correspond with each stroke of the cockroach leg. These are “single-unit recordings,” a sampling of the activity of individual or small clusters of neurons. The sound we are hearing is a burst of activity: the neurons rapidly firing in response to the stimuli, and attempting to send the electrical message up the brain.

Dr. Gage points out the spikes, or action potentials, associated with the firing of neurons in the roach’s leg.

Next, Gage pulls up his screen and shows a visual representation of the electrical signals. Along with the sound, it is clear to see the large spikes that correspond with the neurons firing. These spikes are called action potentials, and they occur when the membrane potential of a specific cell location rapidly rises and falls. When touching the leg hairs with more pressure, the number of action potentials per second increases. Measuring the number of spikes that occur per second is called rate coding, and it can be used to answer complex questions about how neurons respond to stimuli.

This experiment demonstrated how neurons send electrical impulses to the brain. But the brain does not just receive electrical impulses, it also sends them out. What happens if we tried to simulate the electrical impulses sent by the brain to the cockroach’s leg? In his second on-stage experiment, Gage demonstrates exactly this, using hip-hop music from his iPod as his electrical current.

The buds of a pair of headphones are cut off and replaced with small clips that attach to the electrode pins sticking out of the leg. Dr. Gage presses play on the music on his iPod, and immediately, the end of the cockroach leg begins to twitch and jump. The leg moves most dramatically with the bass of the music: lower frequencies have the longest waves, which correspond to the largest amount of current. 

You can watch Dr. Gage perform the “cockroach beatbox” experiment live on stage in one of his Ted Talks.

One final experiment combines both of the previous ones: how nerves encode information, and how nerves can be stimulated. A group of undergraduates at the University of Chile developed a system that uses an app to control the mind of a roach. Cockroaches use their antennae to observe the environment around them. If you take a cockroach and fit a wire inside each antenna (think of them like hollow tubes filled with neurons), you can stimulate those neurons, tricking the cockroach brain into thinking it has detected an outside stimulus. Using an Arduino microcontroller, the team of students created a little “hat” for the cockroach, and connected it via bluetooth to a smartphone app that can be used to send electrical impulses. Stimulating the right antennae causes the cockroach to move to the left, and stimulating the left antennae causes the cockroach to move to the right.

The RoboRoach device uses a smartphone app to perform “mind control” on the roach.

Why a cockroach? It’s a question that a volunteer stops to ask after finding herself up close and personal with the creature. Gage explains that they actually have brains very similar to our own. If we can learn “a little about how their brain works, we’re gonna learn a lot about ours.”

He ends his presentation with a parting message to all the researchers in the room: “I spend my life working on weird things like this, because each one tells a little story. Through these stories we can bring experiments to classrooms, democratize science and make it more accessible to everyone.”

Post by Kyla Hunter

Post by Kyla Hunter, Class of 2023