Researchers in China have reportedly carried out a successful head transplant on a rat.

Italian scientist Sergio Canavero and colleague Xiaoping Ren allegedly attached the head of a smaller rat into the bigger one while maintaining the donor's brain activity. And a third rat was used to maintain the blood pressure on both rats that underwent the operation.

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The experiment was performed on multiple rats, and most of them survive only within 36 hours after the procedure. Despite this, Canavero still hailed the operation a success as it was able to avoid major blood loss.

Canavero has also done a similar procedure to a dog, which suffered from a severed spinal cord, and to a monkey. The monkey survived for only 20 hours, while details on the dog have not been released yet, the Business Insider reported.

Although the survival rate is poor, Canavero still considered the experiment a crucial step towards head transplantation on humans. He said that keeping the animals alive was not the goal, the experiment is merely meant to show that a complete procedure on people in on the horizon. In fact, they will attempt to perform the first head transplant later this year.

"High number of volunteers from all over the world came forward," Canavero said. "The final decision is only made immediately prior to the operation, as it also depends on the body donor, who has to be compatible with the receiver in many ways."

Canavero said a Russian man who is suffering from the degenerative, muscle-wasting Werdnig-Hoffman's disease named Valery Spiridonov was supposed to be the first patient, but a currently unselected Chinese citizen will reportedly undergo the operation instead in Harbin, China.

Meanwhile, several neurosurgeons has disputed Canavero's claims, according to the Independent. On his dog experiment, Jerry Silver, a neuroscientist from Case Western Reserve University, argued that Canavero's papers "do not support moving forward in humans."

And other scientists strong criticized Canavero's plan on human head transplant. Dr. Hunt Batjer, president of the American Association for Neurological Surgeons, said in 2015 that "I would not wish this on anyone. I would not allow anyone to do it to me as there are a lot of things worse than death."