My name is Greg McMurtry. I am a sophomore at the University of Michigan studying mechanical engineering, and I have been working with Backyard Brains for the past four months. Currently, I am working with cockroaches and their descending contralateral movement detector “DCMD” neuron. Current research suggests that this neuron is correlated with the detection of and reaction to approaching objects. To test this, we try to take a neural recording from this nerve using a BYB Spikerbox. We then attempt to stimulate the nerve by shining a flashlight at the cockroach to emulate a change in its visual field. My project has two main goals. The first is to develop and refine an experiment that teaches students about the cockroach’s vision and its DCMD. This experiment will be similar in nature to the neural interface surgery used to transform an ordinary cockroach into a RoboRoach. The second purpose of this project is to see how the insects react to certain approaching objects to gain further insight into what the DCMD neuron does and what its response to external stimuli reveals about insect vision.
The procedure used to conduct experiments on the cockroach’s DCMD required that the insect be placed on its back so that electrodes may be inserted through the neck into the DCMD neuron. These electrodes are then connected to the Spikerbox, which can detect any neural activity. In order to gain clear access to the neck, the cockroach’s head was initially anchored back using a piece of string and tape.
This anchoring process was extremely difficult, and it typically took anywhere from five to fifteen minutes to slide the string under the cockroach’s mandible, pulls its head back, and tape the string down without the head shifting during the process. After this process was completed, the cockroach was usually able to move its head into a position that made it very difficult to insert the electrodes. Even if it did not move its head into a difficult position, the cockroach was able to break free from the string and tape within ten minutes of being anchored, leaving a small time frame to conduct the actual experiment.
Frustrated by the difficulty of anchoring the roach’s head back, I began to think of alternative methods to do the same task. Drawing inspiration from the head immobilizers used by emergency services, I began to sketch potential concepts in my lab notebook.
After encouragement from the BYB team, I began designing a more precise model. I began by taking measurements of the cockroach at various points of its body, measurements of the cork, and measurements of the SpikerBox in order to determine the required dimensions for the holder.
When the to-scale model was sketched, I began designing the first model of the Head’s Up! Roach Holder using Sketchup. After printing and assembling the Head’s Up! Roach Holder, I tested it out immediately to see if it worked and if I would need to make changes.
It worked! I was excited that my initial design not only worked, but also far surpassed the string and tape method. It was able to lock both the cockroach’s body and head into place for over an hour, something that the simple tape and string was unable to do.
As a result of this completely immobilized state, I was able to place the electrodes in near perfect position. Initially, a steady beam from a flashlight did not evoke any bioelectrical response. When the flashlight was placed in strobe mode, faint popping sounds were heard coming from the Spikerbox. Upon further testing and combined with visual confirmation from the recordings from the Spikerbox app, these popping sounds were confirmed to be the DCMD neuron processing and reacting to the visual stimulus.
Though significant progress has been made with this project, there is still much more that has to be done. The Head’s Up! Roach Holder will most likely undergo slight revisions so that its height can be adjusted for cockroaches of varying sizes. Future testing will be done in order to qualify the response of the prep based on the electrode positions. The only problem I foresee is determining and verifying the optimal electrode position to get reliable and consistent readings.
Regardless of any possibilities that lie ahead, this research position will continue to be both interesting and rewarding. Check the blog for an update in April!