Octopuses exposed to “ecstasy” display unusual social behaviour with surprising parallels with human responses to this psychoactive drug, scientists reported on Thursday, nearly 50 years after Beatles’ Ringo Starr wrote and sang lyrics that link octopuses with happiness.

Humans and octopuses are separated by 500 million years on the evolutionary tree. But researchers Eric Edsinger at the Marine Biological Laboratory and Gul Dolen at the Johns Hopkins University in the US suggest that they share responses to the mood-altering drug called MDMA, or ecstasy.

Their findings were published in the journal Current Biology.

“The brains of octopuses are more similar to those of snails than humans, but our studies add to evidence that they can exhibit some of the same behaviours we can,” Dolen, a neuroscientist, said in a media release. “Our studies suggest that certain brain chemicals that send signals required for these social behaviours are evolutionary conserved.”

When people take MDMA, they experience a rush of brain chemicals such as dopamine, serotonin and oxytocin which produce feelings of emotional closeness, making people want to connect with others.

Scientists say studies in the past have revealed remarkable abilities of octopuses — limb regeneration, camouflage, adaptation to temperature and levels of intelligence unexpected in creatures without a cerebral cortex. But Most octopuses are shy and avoid others, including other octopuses.

Through genome studies, Dolen and Edsinger found that octopuses and humans share genetic codes for a molecule that binds serotonin to the brain cells’ membrane that also plays a role in binding MDMA to brain cells. That genetic discovery prompted them to design experiments in which they exposed octopuses to MDMA.

They placed octopuses in a beaker containing a liquefied version of MDMA, which is absorbed by the animals through their gills. The octopuses exposed to MDMA spent more time in the chamber where male octopus was caged and also engaged in what appeared to be exploratory surface contact.

“It wasn’t just quantitatively more time, but qualitative,” Dolen said. “They tended to hug the cage and put their mouth parts to the cage. This is similar to how humans react to MDMA — they touch each other frequently.” The researchers say their findings provide the first evidence that the “procial effects” of MDMA are evolutionary conserved in octopuses.

In 1969, Starr wrote and sang Octopus’s Garden, a song with lyrics that express a desire to visit an octopus’s garden. “We would be so happy you and me/No one there to tell us what to do/I’d like to be under the sea/In an octopus’s garden with you.”

The new research findings, if confirmed, may have applications in medicine. Dolen and Edsinger point out that their studies establish the first drug-delivery protocols for behavioural pharmacology experiments in octopuses and indicate that effective doses of MDMA are in the same range as described for humans.

Their work provides a “proof-of-concept” that could be developed further to use octopuses as model organisms for translational medical research.