Unless you've eaten sannakji, the Korean specialty of semi-live octopus, you might never have had a squirming octopus arm in your mouth.
But you've most likely had a very similar experience. In fact, you're probably having one right now.
Octopus arms might seem strange and mysterious, but they are remarkably similar to the human tongue. Known as muscular hydrostats, both of these appendages can easily bend, extend and change shape (remember that time you had to stretch out your tongue to lick that last bit of chocolate pudding from the bottom of the cup?).
Researchers are hoping a new interdisciplinary project to look at movement in the octopus arm and the human tongue will shed light on how both of these complex structures are activated. This, in turn, could help scientists understand neurological diseases that affect speech, such as Parkinson's.
"The human tongue is a very different muscular system than the rest of the human body," Khalil Iskarous, an assistant professor of linguistics at the University of Southern California who is helping to lead the research, said in a prepared statement. "Our bodies are vertebrate mechanisms that operate by muscle working on bone to move. The tongue is in a different muscular family, much like an invertebrate. It's entirely muscle—it's muscle moving muscle." Both move by compressing fluid in one section of a muscle, creating movement in another part. But we know little about exactly how that movement is initiated and so finely controlled.
Being able to tie a cherry stem into a knot inside one's mouth is a cocktail party badge of extreme human tongue dexterity. But, says Jennifer Mather, a cephalopod behavioral biologist at the University of Lethbridge and collaborator on the project, the octopus has an even greater range of motion. "Theoretically, it can make a knot in its arm and run the knot down its length and off the tip," she noted. Ouch.
For the multi-year study, which is currently getting underway, the researchers will be observing Octopus bimaculoides and O. bimaculatusboth in the wild and in captivity.
The researchers will also include in the study another invertebrate, whose body is a muscular hydrostat--the famous C. elegans roundworm. Scientists know more about this popular scientific subject than the octopus arm or the human tongue, so it will be a useful model from which to start. "We know the number of neurons in C. elegans," Iskarous said. "We know which neuron cells are connected to muscle cells." And with that, "you have a chance at formulating simple mathematical ideas that are linked to movements of the organism and can be measured," he noted.
The researchers will be looking in particular at the use of dopamine and how different levels of this neurotransmitter—which seems to play a role in Parkinson's disease in humans—affect C. elegans's movement. By finding these connections between dopamine and hydrostatic muscle control, "we may have a chance to understand more complex connectivity in an animal like an octopus or a human being," Iskarous said.
Part of the challenge, the researchers noted, will be finding a common language to describe the movement of the human tongue, the octopus arm and C. elegans. They will strive for a unifying mathematical model, but at the outset, the profusion of linguistic descriptors for the flexible human organ already has the octopus researchers a little tongue tied.
To learn more about the amazing abilities of octopus arms, check out Octopus! The Most Mysterious Creature In the Sea.
Illustration courtesy of Ivan Phillipsen