The brain, that eternally mysterious blancmange of grey matter, has become very fashionable these days. That may seem a curious observation, given that our brains have always been at the centre of everything we think and do. But there does seem to be a growing popular interest in all things neurological.

Neuroscience has laid siege to the humanities in recent years, as philosophy and other disciplines have had to fight a rearguard battle against the rising new verities of brain circuitry.

CT imaging scans are everywhere, as illegible to the general viewer as a Rorschach test, but deemed the (often bogus) sine qua non of scientific credibility for all matters psychological.

But perhaps the most interesting development, at least for readers, is the proliferation of books about the brain as a subject of narrative richness. Some, like the neurosurgeon Henry Marsh’s excellent Do No Harm, are focused on the organic frailties of the delicate blancmange; others follow in the illustrious footsteps of Oliver Sacks, by exploring the complex relationship between our brains and our mental and physical behaviour.

Reaching Down the Rabbit Hole, by Dr Allan Ropper and BD Burrell, is very much in the latter tradition. Ropper is a distinguished neurologist at Harvard Medical School. He has many fascinating tales to tell, but he doesn’t. Burrell does. Or at least Burrell is the prose man, turning Ropper’s professional stories into tight little homilies of neurological and existential meaning.

He does it well enough, but sometimes two brains are not as good as one. What makes Sacks’s work so distinctive is his unique voice, at once meticulously precise and yet almost delightfully perverse. To read him is not just an insight into the strange workings of malfunctioning brains but also the strange workings of a particularly high functioning brain: Sacks’s own.

What Burrell and Ropper produce is a portrait of an immensely talented neurologist and teacher who is always the smartest man in the room. Almost every anecdote ends with Ropper emerging the hero of the moment. It’s too carefully written to be crassly boastful, but it’s not exactly an essay in professional humility.

When all his colleagues think a patient is suffering from a brain tumour or a stroke, Ropper knows that it’s herpes encephalitis. He doesn’t need to look at scans. He can tell from a bedside exam.

In a sense, the book is long argument for the primacy of old-fashioned observation over newfangled technology. The central paradox with which it grapples is that in neurology the very means a patient uses to explain himself – ie his brain – is often impaired, and so unreliable.

Yet this unreliability is itself a window into another reality, the distorted Alice in Wonderland world to which the title refers and in which neurological patients are wont to find themselves tormentingly trapped.

There are any number of ways the brain can go wrong and Ropper seems to have encountered them all: meningitis, subarachnoid haemorrhage, embolism, tumours, gliomas, seizures and hemiplegias.

And of course the many catastrophes that hide behind that banal term: a stroke. According to Ropper, the Scandinavians have the lowest rates of stroke in the world, while the healthy Japanese, of all people, have the highest.

I’m not sure that those statistics are entirely up to date, but in any case this is not a book for hypochondriacs or anyone who worries that their difficulty in remembering film stars’ names might stem from something more troubling than unmemorable film stars. Because the fear it plays on, consciously or not, is the sudden and cruel inversion of normality.

Time and again, characters with boilerplate descriptions – “Lucinda H is a Latina female in her late teens … with short-cropped and spiky hair” – announce themselves with bizarre symptoms that arrive, often without warning, in the most mundane situations.

What makes diagnosis particularly challenging is that, being the neurotic individuals we are, sometimes the problem is psychological not neurological. The mind can persuade the brain to suffer everything from paralysis to blindness. Ropper relates that a veteran neurologist advised him to wave a $100 bill in front of anyone showing signs of hysterical blindness – apparently their eyes can’t help but follow it.

It’s one of countless intriguing medical titbits that Ropper and Burrell stitch together in a series of what the subtitle accurately calls “extraordinary journeys into the human brain”.

But where ultimately do these journeys lead? What lies at the other end of the rabbit hole except the uncomfortable knowledge that who we are and all that we hold certain is precariously contingent?

One rogue strip of blood vessel, torn off, perhaps, during a robust neck massage, could impede the flow of blood to the brain and wreak devastating damage on the mass of neurons that govern our lives.

It’s something to think about. But not for too long.

Reaching Down the Rabbit Hole is published by Atlantic (£17.99). Click here to order it for £14.39