12.13.07
Inside the brain of crayfish
Today’s show, from an article published on the Oscar web site written by Fariss Samarrai, we examine lobsters and other crustaceans. What most people think of as food, is being utilized by UVa biology professor DeForest Mellon in his research of how the brain detects, integrates and uses co-joined yet dissimilar sensory inputs.
Imagine you are on a voyage to the bottom of the sea, or simply looking along the bottom of a clear stream observing lobsters or crayfish waving their antennae. Looking closer, you see them feeling around with their legs and flicking their antennules — the small, paired sets of miniature feelers at the top of their heads between the long antennae. While the long antennae are used for getting a physical feel of an area, such as the contours of a crevice, the smaller antennules are there to both help the creature smell and also to sense motion in the water that could indicate the presence of food, a mate or danger. The legs also have receptors that detect chemical signatures, preferably those emanating from a nice hunk of dead fish.
“They constantly flick their antennules,” says DeForest Mellon, a University of Virginia biology professor, “it is doing two things that are processed simultaneously in the brain as he flicks: smelling the water, and also sensing motion in the water, which can indicate the presence of food or other things of interest.” Mellon said, “I’m interested in understanding how these senses are combined and interpreted in the brain of these animals. My question is how does the brain detect, integrate and use these co-joined but dissimilar sensory inputs?”
“We taste food by a combination of senses, taste, aroma, texture and how good that dish looks. This complex process of brain processing is not much different with crustaceans, though their brains are much simpler, which makes them a great study model,” Mellon says. Mellon and other neurophysiology researchers commonly use crustaceans to try to gain basic understanding of the nervous systems of creatures in general. Extrapolating what they find to gain a basic understanding of the much more complex human brain.
Mellon says, “due to the large-sized nerve cells of invertebrates, we can conveniently and practically examine these systems that are largely the same among all creatures, and antennule flicking can serve as a practical model that helps us understand how two or more senses work together in the brain.”
Mellon has been investigating sensory systems for half a century, since his grad school days at Johns Hopkins University. And he’s still learning. Recently Mellon perused the research in the field — his own and that of many other scientists — of the past 45 years or so and published a review of the literature in the August 2007 issue of The Biological Bulletin.
What he’s found is that there is still much to be understood. “It’s fertile ground for ongoing research,” he said. “The size of an area of the brain devoted to a particular sense gives us a good idea of how an animal perceives the world. About 40 percent of a crustacean’s brain is devoted to the sense of smell. This shows how important detecting odors are to the animal.” “Crayfish and lobsters are generally solitary creatures, inhabiting an aquatic environment that is often dark, and they need that highly acute sense of smell.”Humans, by contrast, have less than 1 percent by volume of the brain devoted to interpreting smells, but about 30 percent of the human brain is concerned with visual processing.
Mellon said, “I have always been fascinated by the diversity of animal types and their equally diverse behaviors. Both are genetically based. And through often very subtle adoption of genetic variations in different animals, evolution has arrived at different solutions to common survival problems. This behavioral diversity and the variants in nervous system organization account for why I remain fascinated with biology.”