My quiet, loving wife is now rude, dresses outrageously and pinches men’s bottoms… but

OUR BRAIN, OUR SELVES by Masud Husain (Canongate £20, 288pp)

The neurologist Masud Husain was sitting in a London square, enjoying a rare moment of peace before the start of his working day, when the tranquil atmosphere was rent by a commotion.

A woman in her late 50s, dressed in a pink cowgirl suit and high-heeled crocodile leather boots, was screaming at a coffee vendor. ‘This tastes like drain water,’ she raged, pouring her cappuccino on to the street.

Husain might have hoped never to see the woman again, but she turned up in his clinic that morning.

Introducing herself as Sue, she told the doctor off for running ten minutes behind schedule, then put her feet on his desk, to the horror of her husband Alan.

The thing about Sue, Alan explained, was that she hadn’t always been like this.

Two years ago, she was the warm and affectionate woman he’d married; but lately she had become cold and callous, prone to alarmingly rude outbursts.

Seeing a woman on the street, Sue had told her: ‘You need to lose weight, love. That dress is doing you no favours.’ On a bus, she’d squeezed a young man’s bottom and said: ‘You’ll go far, my lad, with an a*** like that’.

As occurs more than once in this funny, fascinating book, Sue doesn’t think there’s much wrong with her. But after careful investigations, Husain gets to the heart of the matter.

Sue, it transpires, has a condition called behavioural variant frontotemporal dementia, which is known to cause disinhibited behaviour and a loss of empathy. Luckily for her – and for Alan – the edge can be taken off the condition, at least for a while, with certain drugs.

The book is arranged around Husain’s encounters with seven particularly interesting patients he’s treated over the course of his high-flying career.

He also light-footedly explores the science and philosophy of identity, from Descartes’ idea that the self is separate from the brain, to the AI pioneer Marvin Minsky’s theory that the self is simply the product of a collection of different cognitive processes.

Diseases like behavioural variant frontotemporal dementia can change your personality so that you dress, speak and behave differently

Together, these make up the ‘society of our minds’, Minsky argues.

A theme running through the book is how reliant our sense of self is on our brains running smoothly, and how quickly our social standing can slip when they malfunction.

This is rendered heart-wrenchingly clear in the case of Michael, a dapper former City investor who turns up at Husain’s clinic with a fairly minor complaint: he’s having trouble finding the right words for things.

Asked what the term is for a machine that cuts grass,

Michael decides it must be ‘grass cutter’. Asked to draw a garden rake, he draws, with great skill, a toothbrush.

Further testing reveals he is also losing his grip on what objects are for. Presented with a screwdriver, he tries to use it like a spoon; given a hammer, he wields it like a saw.

A scan reveals that the temporal lobe of his brain has shrunk, as is commonly experienced by people with semantic dementia. 

Three years on from the diagnosis, Michael’s condition has deteriorated radically. Husain finds him in the hospital waiting room, tenderly stroking a rubber plant. ‘There there, don’t be frightened,’ he tells it.

His wife says that their home life has become virtually impossible: Michael will eat rotting food from the bin, or attempt to flush clothes down the toilet, possibly because he thinks it’s a washing machine.

More hopeful is the story of Winston, a member of the Windrush generation who is brought in by a friend. To the untrained eye, Winston is a drunk: he bumps into things and can’t walk straight. But Husain has a hunch that something more complicated is going on.

Winston, it transpires, has had a stroke that has left him unable to notice anything that happens on his left side. It’s not an easy condition to live with but, with time, his symptoms begin to ease.

The book left me with a strong feeling that we should treasure the mental and physical health we do enjoy, as they are both vulnerable to sudden lurches in fortune.

This is movingly the case with Anna, a young woman originally from Poland who was beaten up by racist thugs in a park in Ealing at the age of 13. Years later, Anna seems to have recovered, but she comes to Husain struggling with a curious problem: she keeps losing control of her right arm and leg.

Very soon, this gets Anna into trouble. Sitting beside a stranger on a bus, she starts daydreaming, then notices the woman next to her is shouting. Anna looks down and finds that her hand has meandered over to the woman’s thigh – and gripped it hard.

As Husain discovers, a cyst has developed around the brain injury that Anna sustained in the attack all those years ago. When the cyst is removed, she regains mastery of her limbs and can sit on buses without risking the wellbeing of her fellow passengers.

When Husain met Michael, a former city banker, he was having trouble recalling the right words for things. He saw a screwdriver and used it as a spoon, and tried to saw with a hammer

Above all, the book is a reminder of how mysterious the workings of the human brain are.

Wahid, a bus driver, is tormented by hallucinations of hooded men and scuttling mice, which turn out to be caused by a form of dementia.

Trish, a receptionist, has a kind of Alzheimer’s that causes her to become convinced that her partner, Steve, is actually one of several Steves that she’s having a dalliance with.

David, a consultant, has a stroke that causes him to go overnight from being a motivated young professional to someone who spills his food down his shirt and doesn’t care when he loses his job.

The book builds a powerful case for supporting people whose brains have become unruly, rather than isolating them.

In every case Husain presents, the patient in question is alienated in some form from their community: they are deemed a liability or regarded with fearful superstition; they are found to be ‘hard work’.

But rallying around such vulnerable individuals – rather than avoiding them or getting annoyed with them – can be a lifeline.