All Octopuses May Be Sentient, But Only Some Are Smart

The fish in the corners of this image are cooperatively hunting with the octopus, a mark of its intelligence. Image Credit: University of Queensland

The intelligence of octopuses has become legendary, from their slightly unnerving escape capacities to popular documentaries. These feats of brilliance probably contributed to their recent legal recognition in the UK as sentient beings with accompanying rights. However MRI studies of the brains of four species of octopus show there are big variations in the size and texture of their brains that relate to their lifestyles, which means only some of them have this famous problem-solving capacity.

The University of Queensland's Brain Institute possesses an MRI machine far more powerful, and therefore capable of much finer resolution, than those available to hospitals. Dr Wen-Sung Chung put three species of octopus and some vampire squids in the machine and compared them with results others have obtained on other species with more conventional devices. The results are reported in Current Biology

Chung told IFLScience vampire squids, considered a link between squid and octopuses are hard to catch, particularly if you want them intact enough to study their brains. Nevertheless, with specially designed fishing nets Chung and co-authors managed it, revealing these creatures have smooth brains like the less intelligent mammals, befitting a slow-moving lifestyle in a relatively simple environment.

On the other hand, Chung pointed out, the challenges of spotting prey at great depths have led vampire squid to not only evolve very large eyes, but to develop very large optic bulbs in their brains. “We don't know what is happening inside their brains,” Chung said, but visual input is very important.

It is the octopuses that occupy the complex environments of shallow-water coral reefs that have had to learn to adapt to fast-changing situations and anticipate the moves of others. This is reflected in brains that are not only larger for their size than their deepwater cousins, but folded like those of humans and other primates. The increased surface area allows for more complex information processing with the shorter distances across folds making for faster processing, even though total neuron numbers are similar to those of tree shrews.

Despite their reputations as the ultimate loners, reef octopuses can cooperate with other species when it suits them. “These octopuses have some remarkably complex behaviors not known in other octopuses,” Chung said in a statement. This includes hunting collaboratively with coral trout. Chung told IFLScience sometimes the trout will find prey they cannot reach and signal to the octopus, whose tentacles will find their way between rocks or hard corals to flush out small organisms the two can share. It's the marine equivalent of human-wolf cooperation.

A reef octopus and coral trout team up to hunt, demonstrating their intelligence.

For this to work, the octopus needs to be able to read the messages the trout sends. Chung added such behavior has been witnessed from the Red Sea to the Great Barrier Reef, although it has rarely been filmed.

Considering the octopus brain is, in Chung's words, “shaped like a doughnut” it's not surprising their structure is fundamentally different from that of humans. The authors hope their work will open the door to understanding the similarities and differences between the most intelligent representatives of the vertebrate and invertebrate lines.

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