A linguist and marine biologist at the USC Dornsife College of Letters, Arts and Sciences began an unlikely project two years ago to compare the movement of the human tongue with the manipulation of the arms of the octopus and the undulation of a small worm known as C. elegans.
The researchers encountered a problem during their observations — the local species of octopus near Catalina Island did not show up daylight hours. However, the scientists were able to find substitute cephalopods in Japan that were active when the sun was out. As a result, the team had hours of video to analyze, and two USC participants in the study reported their progress at an Australian conference held in August.
Titled “Dynamical Principles of Animal Movement,” the project is supported by the National Science Foundation. Its principal investigators at USC Dornsife are Khalil Iskarous, assistant professor of linguistics, and Andrew Gracey, associate professor of biological sciences.
As a linguist, Iskarous hopes the research will help explain how movements of the human tongue are compromised by Parkinson’s disease, but he said the NSF research is aimed at broader questions of motor control.
“When we’re trying to accomplish a physical task, such as reaching for something, it is in three-dimensional space, and we require the coordination of muscles and joints to achieve that task,” he said. “Our muscles and joints have many ‘degrees of freedom’ — they can be flexed or extended in different ways to accomplish a task — and we’re asking how the motor control system of an animal, including a human, will reduce those degrees of freedom to manage things in the environment.”
Iskarous and his colleagues want to know how the process of reducing degrees of freedom unfolds and how it can be quantified.
Getting octopus on camera
The original subjects for the octopus observations are two closely related species — Octopus bimaculoides and Octopus bimaculatus — that live in the waters near the USC Wrigley Marine Science Center on Catalina Island. These local cephalopods hunt at night, but the available light was unsuitable for video recording. The octopus experts on the research team subsequently found replacements with help from Japanese colleagues at the Okinawa Institute of Science and Technology and the University of the Ryukyus.
Ikeda Yuzuru, a cephalopod expert on the faculty at Ryukyus, and his graduate students directed the USC team to a Japanese reef inhabited by octopus of the genus Abdopus. The team members traveled to Okinawa last year, and they spent weeks wading through the water at low tide with high-definition GoPro camcorders mounted on selfie sticks.
“We wanted to take as much video as we could of natural octopus behavior,” said Jean Alupay, a marine biologist and postdoctoral scholar in the USC Dornsife departments of linguistics and biological sciences. “We videotaped for the entire low tide. We were out there for about a month, recording all of these animals in natural behaviors in a foot or less of water.”
Alupay said the researchers captured mating behavior, defensive behavior and a particularly interesting “arm slapping” behavior of an octopus during an extended “interaction” with a goby fish. The octopus appeared to be whipping one of its arms at the fish, an action that likely involves visual perception to direct the slapping behavior and then the physical action of curling its arm and rapidly extending it.
Using calculus for comparisons
The researchers are enhancing the octopus video to show the outlines of their arms when they’re in motion and to place coordinates along those outlines for interpretation using calculus.
“Calculus allows us to look at basic ideas of curvature and change — temporal change and spatial change,” Iskarous said.
Calculus will allow comparison of octopus movements to other subjects in the NSF research project — including C. elegans, a tiny nematode worm. USC Wrigley Institute faculty member Gracey is studying the worm to determine the connection between its genetics and its behavior.
C. elegans measures 1 millimeter end-to-end, and decades of research have documented the characteristics of every one of its 959 cells. Gracey and Iskarous are particularly concerned with cells in the worm that process dopamine, a neurotransmitter that influences movement and motor control.
Later this year, Iskarous will begin work to analyze the movement of the tongue and the production of speech based on observations of people, including those with Parkinson’s. He’ll work on this phase of the project with Shrikanth Narayanan, professor of linguistics, psychology and neuroscience at USC Dornsife and professor of electrical engineering and computer science at the USC Viterbi School of Engineering. Together, they will compare the movement and curvature of the human tongue to the movements of the worms that have undergone modifications to their neural circuits.