The Hamster's addicted to celery

They were right. Although fine in every other respect, the "Hamster' has developed a fixation on celery.

Despite his nickname, the Top Gear presenter always loathed the vegetable. Yet since suffering a head injury in the 300mph crash in September, the 36-year-old has been eating it every day, to the amazement of his friends and family.

And they are even more puzzled by another change in the TV daredevil - his sudden and astonishing ability to recall his bank-card PIN.

Hammond had forgotten the PIN for a card he received before the crash, having seen the code only once. But on a recent visit to a cash machine, he found he automatically punched in the correct number.

Brain experts say the side-effects that Hammond has experienced are extremely unusual. Most people who have head injuries find it difficult to concentrate and hard to remember things.

Head injuries can have other strange effects, including Foreign Accent Syndrome, usually associated with strokes.

One sufferer, Linda Walker, lost her Geordie accent after suffering a stroke in July, waking up to discover she was speaking with a Jamaican twang.

But the good news for Hammond is that his new powers of recall - and liking of celery - will probably not go away. Changes tend to become permanent after about three months.

Hammond's friends admitted they were mystified. His spokesman Gary Farrow said: "It's very odd. He hated celery before the accident. He wouldn't have it in the house and he couldn't bear the thought of eating it. But now he loves it. It's in his daily diet."

Leading neurologist Professor Derick Wade, of the Oxford Centre for Enablement, said cases of changing food preferences were extremely uncommon.

"It's not something that is usually asked about,' he said. "I do come across cases in passing but there would be less than one a year out of several hundred cases."

Prof Wade also said that Hammond's recall of his PIN was surprising.

"Memory is usually impaired, particularly for things that have no pattern, such as PINs which are incidental or incoherent,' he said. "Memory is not linked to any specific area of the brain. This would merit further study."

One theory is that Hammond may be taking medication that is improving his powers of recall.

A study published by the New York University School of Medicine in September showed that a drug used for dementia could improve memory in brain-injury patients.

A breakthrough would be significant for those suffering from the many memory problems related to brain injuries.

The most common conditions are aphasia, the inability to remember words, anomia, the 'tip of the tongue' difficulty with naming things, and apraxia, where patients 'forget' how to make certain movements, such as walking.

More unusual problems include Capgras syndrome, where sufferers are convinced their loved one has been replaced by an impostor.