A semi-anaesthetised 56-year-old man lies on the operating table, murmuring half-responses to the blue-gowned group that surrounds him. Consultant neurosurgeon Neil Kitchen stands over him, flanked by the anaesthetist, two registrars and theatre staff. As the patient drifts off to sleep he is told to "think of sunshine in Hastings". Nothing could convey the atmosphere in this room less.

Sitting apprehensively in the corner, I too am dressed from head to foot in blue, complete with cap and rubber clogs - the obligatory uniform of the operating theatre. Few of us are ever allowed to witness an operation, so this is a rare opportunity. All the same, it is with quiet relief that I learn today's procedure at the National Hospital for Neurology and Neurosurgery in London will not involve a craniotomy - cutting open the skull.

As the doctors and theatre staff wait for the patient to "go under", Kitchen shows me the long insulated needle he will insert in the man's cheek, through a hole in the skull and into the trigeminal nerve - the largest cranial nerve responsible for sensation in the face. Machines beep continuously, and monitors glare.

Acutely focused but calm, Kitchen performs the operation, occasionally glancing up at a "live" x-ray scan of the needle deep inside the patient's head. Kitchen and his anaesthetist then wake the man up - a slow process - and ask him to confirm whether or not the needle is in the right place. More sleepy murmurs. Finally, a further injection of anaesthetic is administered before a heated electric probe is used to cauterise the nerve.

The whole process takes 20 minutes and is designed to remove the all-consuming, acute facial neuralgia (pain) the patient, who has multiple sclerosis, has been experiencing. This "simple procedure" is known as radiofrequency thermocoagulation of the trigeminal nerve, explains Kitchen, who specialises in disorders of the skull base, a complex area involving tumours and vascular problems.

Simple is not the most obvious word used to describe brain surgery. Yet despite his advanced, often life-saving, work, Kitchen remains humble. "One is very privileged to be able to do this," he says.

There are, however, patients whom his surgical expertise may not save. "People with very bad malignant brain tumours, who present 'end-stage', in a coma, for example", says Kitchen. "It's very frustrating dealing with patients, when you think you've done a great job, but actually you're defeated by the condition."

I'm guided through the intensive care unit, which, Kitchen says, has a serious bed shortage. Here there are patients on ventilators, but also a man who was admitted while in an end-stage coma - the result of a brain haemorrhage - but who is now making a miraculous recovery following surgery. Restoring people to health is naturally "a great feeling", says Kitchen, but "there's quite a dependency on you and you can't switch off."

With its millions of cells and trillions of connections, the brain is still the most complex supercomputer in the world. One small slip can alter a person permanently. Does Kitchen worry? "Absolutely. It's very unusual for a technical error to occur. It just doesn't." I study Kitchen's hands. They are reassuringly steady.

Also, quite large amounts of the brain can be removed without any "obvious" clinical side effects. Humans are commonly said to use only one tenth of their mental capacity. "You would have thought we should be able to train ourselves to use the whole of our brains and be better people for it," says Kitchen. "The brain is the most complex thing in the known universe. We are basically highly trained mechanics. When it goes wrong we've got to fix it."

Modern advances in neuroimaging have allowed us to better understand which parts of the brain control movement, sensation, speech and vision. But the areas responsible for emotions are less well known. "That's a more diffuse network and we haven't really pinpointed that yet," says Kitchen.

I can't help imagining that being a neurosurgeon must give you a particularly clinical view of emotions. "If you're doing an operation and you've done your craniotomy and you just see the brain sitting there, that is that person, that is the human," he says. "Yes, it's very bizarre. It does give you a very materialistic view of existence, but the other side of human consciousness, which we can't explain, is just so incredible."

So where is the mind? "Who knows?" says Kitchen, who is not a religious man.

Having been a consultant for the past 11 years, Kitchen, at the age of 45, is at the peak of his profession. "I'm at the stage where I'm still healthy enough to be up to the job and I'm at cruising speed. You do have to be in good health physically and mentally and you do need to be quite a balanced individual."

An ability to compartmentalise the emotional vicissitudes of one's personal life is a prerequisite for the job. It is the information about patients that constantly circulates in Kitchen's mind. He likens this to plate-spinning. "You have all these people swirling around, so you get quite good at multitasking and prioritising," he says.

I notice these last two skills in Kitchen from the off. Despite just emerging from a meeting, he is able to launch straight into a description of his job for precisely an hour and then leave for his evening ward rounds.

The following morning, he tells me he finished work the previous day at 8.30pm, but was on call during the night and was woken several times with queries. He then rose at 5.30am and jogged to work - his preferred method of transport on operating days, cycling the rest of the week. He is scheduled to perform three operations that morning. The afternoon will be taken up by six hours of meetings about the hospital's five-year plan. With luck he'll be home by 8pm, and in bed by 10pm.

For all this he looks super-fit. The reason, I discover, is that he is also practising to run triathlons. "I do like to do that type of thing because it's a challenge for me," says Kitchen, who has been told by his wife, a palliative care nurse at Barts Hospital, to spend a little bit more time doing nothing.

Despite time constraints the family, which includes two teenage sons whom he took to see Arsenal play on Sunday, are in close contact during the day. "We text each other all the time," says Kitchen. "I'll also speak on the phone every day to find out how things are going."

His hectic working life has already been immortalised in a best-selling novel, Ian McEwan's Saturday. The author shadowed Kitchen for 18 months before writing the novel, in which the central character, Henry Perowne, is a neurosurgeon. Kitchen says the neurosurgical aspects in the book are very accurate, so too "the description of the men's changing rooms. I felt very involved in the evolution of the surgical side of the story. I enjoyed it." But unlike Perowne, Kitchen says he does not scan strangers he meets on the street for neurological afflictions.

In the 11 years that Kitchen has been a consultant neurosurgeon, operations have become less invasive. "Patients are doing better," he says. "A lot of radiology is replacing surgery. I think the trend is for much more minimally invasive work. We've learned that big operations aren't a good idea." Aided by MRI scans, for example, surgeons can now see exactly where the edges of tumours are.

Neuro-oncology is constantly evolving and training the next generation of neurosurgeons is a large part of Kitchen's job. This is particularly time-consuming and needs to be. "To teach someone to do a craniotomy you have to be there with them," he says.

At the top of his game, Kitchen has nowhere else to climb professionally. "There's no formal career structure beyond being a consultant," he says. When and if his interest or health wanes he will happily retire. "I won't be one of those people that hang around the department," says Kitchen. "We'll probably retire up to the Lake District."

Curriculum vitae

Current position

Consultant neurosurgeon and associate clinical director, the National Hospital for Neurology and Neurosurgery

Qualifications

BSc History of Medicine + MBB Chir (Cambs); MD; FRCS (surgical neurology)

Career high

"Being appointed to the National Hospital. I felt it was all I could ever want."

Career low

"There were low points in training because you are not your own person. I much more enjoy being a consultant than I do a trainee."