The brain doesn't look like anything you've seen in zombie movies or in scientific pickling jars.
Its surface is very shiny, like cling-film, covered in cerebrospinal fluid in a thin transparent membrane, explains one of Britain's foremost neurosurgeons, Henry Marsh.
"If you are in the brain and operating on it then it's just like white cream cheese and it's all convoluted, you have all these crevices and cracks in it, albeit covered with thousands of fine blood vessels."
Marsh has prised tumours from these reaches for more than 40 years as a leading neurosurgeon and still has no idea how that mass - the most complex of the body's organs - gives rise to consciousness, thought and feeling.
"That is us, that is the real self, and we are clueless about it.
"When operating with a patient under local anaesthetic, which I specialise in doing, I can have the patient talking. I'm looking at the patient's face and at the same time looking at the parts of the brain doing the talking.
"Intellectually and rationally I know it but emotionally I can't feel or think that the sort of blob in the patient's skull is the real person. Everything we are, are our brains and it's a very strange thought."
Marsh's willingness to concede doubts, anxiety and even fallibility makes him unusual figure in the medical profession and has resulted in an unlikely second career as a non-fiction writer.
He is the author of Do No Harm: Stories of Life, Death and Brain Surgery, his diary from his days as a senior neurosurgeon at St George's Hospital, London, and it is a Sunday Times and New York Times bestseller.
Admissions, his latest, reflects on his 40 years working on the surgical frontline squeezed between patients' hope for miraculous recovery and the coarse and crude limitations of the scalpel.
Marsh likens the comparative skills of a neurosurgeon and neuroscientist to the relationship between "plumbers and physicists working on quantum mechanics and how electrons move in metal".
And yet surgeons are often treated as God-like miracle workers. "That's why I wrote this book - to say we are not," Marsh says. "I like to think my books help patients understand doctors and maybe help doctors understand themselves. The beginning of wisdom is not the fear of the Lord, it's being honest to oneself about mistakes and how one can do better next time."
Medical decisions to treat, investigate and operate are based on an assessment of probabilities, not certainties. While there can be wonderful triumphs there are disasters too, and they form the "larger headstones" in Marsh's "inner cemetery".
Brain surgery is dangerous to patients and Marsh points out that there are 7000 people in Britain in a persistent vegetative or minimally conscious state, hidden away in nursing homes or cared for at home, part of a "great ocean of suffering we tend to avert our eyes from".
Since retiring from full-time work in the National Health Service three years ago, Marsh continues to operate and lecture in Nepal, Albania and Ukraine. In Ukraine two weeks ago, he looked down a line of children with fatal brain tumours.
"I find it particularly upsetting telling their parents there is no hope but then I end up doubting myself and asking: 'Am I absolutely certain about it?' It comes with the territory, that's life and you have to get on with it. Most doctors don't want to do neuroscience because the work is very grim and you see many terrible things."
And yet it is from these mistakes that surgeons learn. "It's terribly important you do torture yourself a bit if you are to retain your humanity, and feel sorry for your patients."
He operated on one of those dying children, who was the same age as his granddaughter. "If I felt for that child I was operating on as if she was my own granddaughter I couldn't do the operation, I would be a nervous wreck," he says.
"So you have to keep detached but not become callous and too detached. It is very important that it does hurt and you do remember your mistakes. Success is bad for us, it makes a surgeon complacent and corrupt, or can do. Surgeons can become corrupted because patients want them to be gods, because that's how we patients deal with our extreme anxiety."
Marsh came to medicine after completing a degree, from Oxford, in philosophy, politics and economics. It was his experience as a theatre porter that made him want to become a surgeon and it was the diagnosis of his son's tumour at three months old that partly influenced his decision a year later to specialise in neurosurgery.
"It gave me some understanding how awful it is when members of your family are undergoing major surgery. A lot of doctors don't know that because they haven't had the personal experience."
Marsh retired in 2014 having pioneered in 1988 the technique of awake craniotomy used for treating low-grade gliomas near speech and visual areas of the brain. It is now standard practice in most neurosurgical departments. The female patient is still alive and well, "which is rather nice".
But his career ended in some minor controversy, he writes, when he got angry with a nurse who had unnecessarily inserted a naso-gastric tube in one of his patients. He tweaked the nurse's nose for which he ruefully apologised. Time, he concluded, to pack up.
On his first visit to Australia for this week's Sydney Writers' Festival, Marsh is keen to get a conversation started on hospital building design as well as the clay feet of the medical fraternity.
The popular configuration of wards and nurses' and doctors' stations more closely approximates a prison than a health centre, he complains.
The busy hospital ward where most of us are doomed to die are even more impersonal than the Nightingale wards of the last century, says Marsh.
"The physical experience of being in a hospital is very unpleasant. The last thing you get as a patient in a hospital is peace, rest or quiet. There is no peace or quiet at night and in the National Health Service, you are in a room with four to six other patients because of the lack of single rooms.
"I have a basic feeling people will get well and recover better if they're in a more therapeutic environment and that means access to the outside world, fresh air and sunshine, and single rooms."
A shortage of government funding is stopping the necessary redesign but so is a top-down attitude in health-care management where patients are considered a "breed of prisoners".
"Particularly doctors often feel threatened by patient autonomy and patients saying what they want. It's a power politics in some ways."
Having spent many years cutting into brains, Marsh says he is deprived of the consolation of a divine creator.
The frontal lobe is responsible for memory, language and impulse. The right governs imagination and creativity and the left written language, logic and reasoning. The midbrain keeps us conscious.
Damage to the frontal lobe can fundamentally alter a person's personality for the worse.
"This is where our social moral forecasting planning functions reside and people with the front of their brain damaged suffer personality change. What we would regard as the true self - the moral social part of us - is changed by physical damage to the brain.
"Once you've seen someone whose fundamental personality and moral nature has been changed for the worse it's very hard to believe that consciousness is not created by the brain.
"When we die, our brain dies and therefore that's the end, and the likelihood of an afterlife seems very unlikely to me. It doesn't feel like it but everything you are thinking and feeling is the electrochemical activity in your nerve cells."
Like any organ, the brain ages as the circuits slow and Marsh's greatest fear is that he might succumb to dementia as his father did. "I'm horrified by the thought."
Marsh jokes that his most precious possession is his "suicide kit", comprising a few drugs well past their use-by date. "Whether they'd work or not I don't know, whether I'd take them or not, I don't know.
"It's a sort of joke but a serious joke because we do find it very hard to talk about death and dying can be very unpleasant. If you are dementing you might forget where you put it."
The dying, Marsh observes, continue to clutch to hope until we "finally turn our face to the wall and give up the ghost", he writes in Admissions. Somewhere in that cream cheese blob, each of us are hardwired for hope.
Henry Marsh is appearing at the Sydney Writers' Festival, May 25-May 27.
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