WASHINGTON (AFP) — Mother monkeys permanently separated from their newborns sometimes find comfort in plush toys: This recent finding from Harvard experiments has set off intense controversy among scientists and reignited the ethical debate over animal testing.

The paper, "Triggers for mother love" was authored by neuroscientist Margaret Livingstone and appeared in the Proceedings of the National Academy of Sciences in September to little fanfare or media coverage.

But once news of the study began spreading on social media, it provoked a firestorm of criticism and eventually a letter to PNAS signed by over 250 scientists calling for a retraction.

Animal rights groups meanwhile recalled Livingstone's past work, which included temporarily suturing shut the eyelids of infant monkeys in order to study the impact on their cognition.

"We cannot ask monkeys for consent, but we can stop using, publishing, and in this case actively promoting cruel methods that knowingly cause extreme distress," wrote Catherine Hobaiter, a primatologist at the University of St Andrews, who co-authored the retraction letter.

Hobaiter told AFP she was awaiting a response from the journal before further comment, but expected news soon. Harvard and Livingstone, for their part, have strongly defended the research.

Livingstone's observations "can help scientists understand maternal bonding in humans and can inform comforting interventions to help women cope with loss in the immediate aftermath of suffering a miscarriage or experiencing a still birth," said Harvard Medical School in a statement.

Livingstone, in a separate statement, said: "I have joined the ranks of scientists targeted and demonized by opponents of animal research, who seek to abolish lifesaving research in all animals."

Such work routinely attracts the ire of groups such as People for the Ethical Treatment of Animals, which opposes all forms of animal testing.

This controversy has notably provoked strong responses in the scientific community, particularly from animal behavior researchers and primatologists, said Alan McElligot of the City University of Hong Kong's Centre for Animal Health and a co-signer of the PNAS letter.