Cephalopods—the class of fascinating animals that includes octopus, squid, and cuttlefish— are the most intelligent, most mobile, and the largest of all molluscs. These ‘brainy’ invertebrates have evolved suckered tentacles, camera-like eyes, color-changing skin, and complex learning behavior. Among the invertebrates, cephalopod brains can’t be beat. For years, these tentacled geniuses have been constantly studied to understand the human nervous system.
Jade Zee, who directs Northeastern University’s program in behavioral neuroscience, talks about what these animals can teach us. “Among invertebrates, they stand very much apart. They’ve evolved a much larger nervous system,” says Zee. “Their body plan is completely different from ours, but they share many of the same fundamental principles in how the nervous system actually underlies behaviors.”
“Neuroscience has really benefited from cephalopods,” says Zee. “The very first action potential, which is the electrical activity of a neuron, was recorded in a squid.” Scientists are particularly interested in the cephalopod axons, the part of a nerve cell that transmits messages away from the cell body. These axons are similar to those found in humans. It’s about a millimeter in diameter and big enough to be seen without a microscope.
Although you may think a millimeter is still pretty small, it’s actually really, really big compared to other nerves. “We humans have white matter, which causes electrical signals to travel much, much faster in our neurons. Invertebrates don’t have that. So the invertebrate solution, if you want electrical signals to travel faster, is to have a wider diameter axon of a neuron.” Zee explains.
Neurons encode information with electrical signals, such as action potentials. They transmit that information to other neurons through synapses. For these animals, the behaviors that need to happen fast would generally be escape behaviors. Having this giant axon that is wider and thicker would allow electrical signals to travel faster in their bodies, and that would help them escape dangerous situations or predators.
Though studying cephalopod brains started out as just a way to understand nervous system physiology, it has really branched out. Zee talks about some experiments that scientists are conducting in the “Neural Systems and Behavior” course that she co-directs. These experiments involved testing ecstasy on a solitary species of octopus which led to surprising results. Just as with humans, ecstasy promoted pro-social behaviors in the octopus too. They started being less interested in toys and more interested in each other. Zee says they hope to apply their findings to develop solutions to human diseases and disorders that affect the brain.