The rapid recovery of Top Gear presenter Richard Hammond after his high-speed car crash has amazed the public and medical experts.
Mr Hammond is recovering in hospital
Only nine days after his 300mph jet-powered car crashed during filming, Mr Hammond is walking and talking and off emergency care.
But his progress over the next six months is likely to be much slower and the outcomes less clear, say doctors.
The TV star will continue his recovery at the Bupa hospital in Bristol.
Slow, difficult period to come
Neurosurgeon Stuart Ross, who looked after Mr Hammond at Leeds General Infirmary in the days following his accident, said rest could help Mr Hammond recover from his "brain injury" within months.
But he said: "There comes a period now which is unfortunately slow and is difficult to get through."
He was hopeful that, with time, Mr Hammond would "be back to his old self".
Dr John Freeland, consultant neuropsychologist from the Brain Injury Rehabilitation Trust, said it was too early too tell what the long-term future would hold.
In high speed crashes, the passenger's body goes from travelling extremely fast to a sudden halt. The body and head are thrown forwards and back, and the brain follows, striking the bony skull.
"We can assume that most of the damage was to the white matter - the communication wires of the brain. Doctors call this diffuse axonal injury.
"These take a beating in these high-speed accidents when the brain is decelerating. The brain is stretched and these communication fibres break up and the cells die off.
He said structures at the front of the brain would be bruised and damaged, where the brain hits the uneven inner surface of the skull above the eyes.
"The brain is soft and gelatinous - its consistency is something between jelly and cooked pasta.
"It is well designed to sustain a direct blow but our genes never imagined we would be travelling at these super-high speeds."
He said that high speed motor vehicle accidents were particularly dangerous because the brain could suffer injuries when the head rotates during the crash.
"Studies show it takes 10 times less force if the brain is able to rotate in these injuries to create the same amount of brain damage.
Richard Hammond left Leeds in the air ambulance on Thursday
"Mr Hammond was lucky because he was in a seven-point restraint system rather than a three-point system that most of us drivers are used to, and his helmet was strapped to restrain the head and stop the rotation."
Also, the fact that the car rolled rather than crashing into a stationary object, such as a brick wall, may have lessened the blow, he said.
The nature of Mr Hammond's brain injuries thankfully mean that functions such as speech, movement and breathing were unaffected, said Dr Freeland.
The frontal lobe is critical for more subtle functions, like personality and ability to make judgements.
"The difficulty with these diffuse white matter injuries is often the big challenges aren't so much walking and talking, but losing quickness and mental flexibility and a some of the personality and character features that we develop from the age of 12 onwards.
"The big question is always how some of those characteristics survive such an injury."
Dr Freeland said he had seen patients with similar brain injuries recover from comas with very little lasting damage. But he said he had seen others with lasting changes.
He said the focus of Mr Hammond's treatment over the next six months would be rehabilitation - making sure his balance is back and he is able to do learned everyday activities that people tend to take for granted, such as doing up buttons.
He said doctors would also be monitoring Mr Hammond's cognitive and emotional state.
"Character and personality changes are fairly pervasive with motor vehicle accidents," he said, but added that the brain was changeable or "plastic" and repaired itself over time to varying extents.
"Much of the wiring of the frontal lobes occurs in puberty. Some of the hardware systems are maturing through to our 20s. The software - developing our self-awareness and how to fit into the social fabric - is very gradual, over decades.
"Recovery from these injuries does continue, but it takes time," he said.