Scientists have transplanted the head of a rat onto the back of another, ahead of a controversial plan to carry out the world's first human head transplant later this year.

In the experiment, scientists transplanted the head of the smaller rat onto the back of the larger rat, creating a two-headed animal.

The animal lived an average of just 36 hours, according to the research paper that was published to CNS Neuroscience and Therapeutics.

The paper was written by a team of Chinese researchers, together with Italian neurosurgeon Sergio Canavero. The latter has, in recent years, gained a level of notoriety for his TED talks, and claims of plans to perform a human head transplant later this year. However, physicians worldwide doubt that a human head transplant is possible on such an advanced timeline.

Image: cns neuroscience and therapeutics

Image: CNS NEUROSCIENCE AND THERAPEUTICS

Three rats were used for the operation — a smaller rat who acted as the donor, and two larger rats.

One larger rat acted as the recipient of the operation, whilst the other provided a continuous blood supply to the donor rat's brain tissue. The donor's head's blood vessels were later attached to the recipient's.

According to the paper, the donor head was still able to blink and respond after the operation.

Canavero first proposed the idea of head transplants — where a living person’s head would be attached to a donor body — in 2013, after a controversial operation in which the whole head of a monkey was transplanted onto a different body.

The monkey was kept alive for 20 hours, for "ethical reasons," the surgeon told New Scientist.

The idea of this procedure however, has caused a fair amount of controversy.

"This is such an overwhelming project, the possibility of it happening is very unlikely," Harry Goldsmith, a clinical professor of neurological surgery at the University of California, Davis, told news outlet New Scientist.

"The real stumbling block is the ethics. Should this surgery be done at all? There are obviously going to be many people who disagree with it.”

Earlier last year, Canavero announced that he had a VR system that would prepare patients for the shock of looking down and seeing someone else's body.

Canavero predicted back in 2015 that the world can expect the procedure to be ready by 2017.