Controversial neurosurgeon Sergio Canavero has said plans for a human head transplant are on track for 2017 following a successful experiment on a dog, where 90% of its spinal cord was severed and re-attached. He and scientists from across the globe also claim to have performed operations to fuse spinal cords on mice with a success rate of just over 50%.

In three studies and video footage released to New Scientist, researchers provided details on how they managed to fuse the spinal cords. However, experts not involved in the experiments who have been shown the research have failed to be convinced and have raised concerns over the techniques used.

Canavero announced his plans to carry out the world's first human head transplant in 2015. Shortly after, Valery Spiridonov – a 31-year-old Russian man suffering from the degenerative Werdnig-Hoffman disease – volunteered to be Canavero's first patient.

While details of the operation have remained scant, Canavero says it would involve cooling down the patient's head to around -15C. The heads of the patient and donor would be severed and the patient's would be attached to the donor. Finally the spinal cords would be fused together and muscle blood supply would be established. The patient would be kept in a coma for around a month to stop movement. Electrodes would be used to stimulate the spinal cord.

sergio canavero
Sergio Canavero hopes to carry out the world's first head transplant surgery in 2017 IBTimes UK

In three papers, edited by Canavero for the journal Surgical Neurology International, scientists from South Korea and the US show how they have carried out experiments on animals involving severing the spinal cord.

Fusing the spinal cord will be one of the major barriers in performing a head transplant. Thousands of neurons need to join together – as if they do not, they cannot send nerve impulses, connecting the brain and the rest of the body.

In one study by scientists at the University in Seoul, 16 mice had their spinal cords severed. Eight were treated with a chemical called polyethylene glycol (PEG), which is thought to help reconnect the spinal cord. PEG was injected into the space between the severed spinal cords. After four weeks, five of the eight mice had regained some movement. All the others died.

In another study, scientists at Rice University in Texas added graphene nanoribbons to provide a scaffold along which neurons can grow. Using this with their PEG technique, the South Korean team showed how there was some electrical activity a day after the spinal cord was cut. Four of the five mice treated died in a flood, but the final one was able to walk and feed itself two weeks after the treatment.

Warning: Contains footage some viewers may find upsetting

Finally, the team tried this technique on a dog. They severed over 90% of its spinal cord then treated it with the graphene/PEG technique. After three days, the team said there was some movement. After two weeks, it could drag its back legs by its torso and front limbs. After three weeks, it could walk.

But Canavero's critics are not convinced. Jerry Silver, a neuroscientist at Case Western Reserve University in Ohio, told the magazine: "The dog is a case report, and you can't learn very much from a single animal without controls. They claim they cut the cervical cord 90% but there's no evidence of that in the paper, just some crude pictures." On the mice study, he added: "You don't report that four of your five treated animals drowned. You start again and increase your sample size."

Arthur Caplan, from New York University, said the results produced would suggest the team are at least three years away from repairing a human spinal cord and that "it would put them maybe seven or eight from trying anything like a head transplant".