Mamie Baird Magnusson made her living with words.

She played with them, prodded them, pulled them into shape. She married a man, Magnus, who did the same. They met in a newspaper office where she was the star writer. They wrote newspaper articles and books (sometimes she wrote books and published them under his name). Even when she was a mother and had five young children around her feet she continued to write. Year after year, words poured out of her. Year after year.

And then slowly, insistently, painfully, words deserted her. She couldn't write them down any more. She eventually lost the ability to read them. And she struggled to even find the ones in her head that she wanted to say. Dementia stripped words away from her.

In the end she could not have written her own story. And so her daughter has done that for her. Or maybe, as Sally Magnusson says, not for her mum but for herself. "Part of the reason I was writing was to hold on to my mother and the very process of finding the words to do that did keep her with me."

Broadcaster Magnusson and I are sitting in the BBC Scotland building at Pacific Quay in Glasgow talking quietly about her late mother, the illness that struck her down, and the heartbreak that came in dementia's wake. "It's bewildering," she says of Mamie's illness, "and it seems utterly, utterly pointless. And when you're in the middle of it you can't see anything except darkness really."

The words to describe that experience came after, an attempt to impose order on the "chaos of the experience", to pierce that darkness. Because words are what Magnusson makes her living with too. Writing is part of the family narrative. "Absolutely and we're a very word-obsessed family. You can imagine living with my father - arch-pedant. Words were always discussed and enjoyed and played with and sung."

And so she has written a book, Where Memories Go, which is both a painful, heartfelt memoir and a call to arms against the illness that killed her mother. Words of grief and words as weapons, you might say.

This is a story about mothers and daughters. This is a story about life and death. And, because they are all death leaves us with, this is also a story about memories; about how they make us who we are. And it's a story that begins - if there is a beginning - with a swimming cow.

In 1999 Sally Magnusson, her mum Mamie and her daughter Anna-Lisa went off to Mull to try to find out more about their ancestors and to see if there could be any credence in the family myth from the time of the Clearances that the family cow, confiscated by landowners, swam back home from Calve Island across the Sound of Mull.

It was an adventure that saw her 73-year-old mother, still full of "girlish vigour", striding into the forest in the summer heat. Fully herself. Only ...

Only there was this night on the island when Mamie knocked on her daughter's door to tell her she had been locked out of her room. They laughed about it but Sally couldn't help noticing that her mum wasn't wearing her pyjama bottoms. A small thing. But, because she was keeping a diary at the time, something Magnusson recorded and then went back and worried over. Was this the beginning of her mother retreating from her? "It is always later when you look back and go 'well, what were the patterns, what was different,'" Magnusson tells me. "And you're reading these notes and you're thinking 'it was around that time, wasn't it?' And I've forged for myself a beginning because I needed to have one.

"But if I'm honest I don't think I was particularly thinking about it or worrying about it. It's all so slow and so much of the change is noted in hindsight rather than at the time."

Eventually, though, the word dementia would rear its ugly head. In 2004 a matron in a care home they were considering for Mamie's sister Harriet, who was suffering from the disease, told Magnusson that her mother has it too: "The signs are all there."

The decline would speed up after Mamie's husband, broadcaster Magnus, died in 2007. A trip to hospital for a hip replacement not so long after didn't help as Mamie was left on her own, confused and uncertain, her children locked out. If she could change anything, Magnusson says, she'd change that hospital policy. "In hospitals the families of elderly people with dementia should be treated the same way as families with young children. If your child goes into hospital you'd be considered a bad parent if you didn't stay with them."

In the end Mamie didn't go into a care home. Instead, she stayed at home, looked after by her family. Mother and daughters changed positions.

Ask Sally Magnusson about motherhood (she has five children of her own) and she talks about her mother. "I probably learned everything I know about motherhood from her and consciously tried to model myself on her. She didn't work as I have. I'm more of a product of the next generation. She did a lot of freelance writing. The typewriter was always clacking away. But she absolutely threw herself into motherhood with great gusto and verve and having had her career as a newspaper reporter and thrown herself into that, it was 'right, now I'm doing motherhood' and so she was hands-on. Not hugely domesticated."

And are you? "No and I don't have a twin sister." (Mamie's twin sister Anna did much of the domestic heavy lifting in the Magnusson household in Rutherglen.) "But fortunately I've got a husband who liked going to Tesco more than I."

Her memories of her mother are, she says, of joie de vivre. "And hard-won joie de vivre," she adds. In May 1973, just a couple of weeks after his 12th birthday, Magnusson's brother Siggy was hit by a lorry. He died three days later. Mamie hid her grief but at night she howled on the bedroom floor with her foot against the door to keep anyone from coming in." The cataclysm of that event hit hard. But it didn't end her love of life. "It wasn't a banal joyousness," Magnusson believes.

Years later, Mamie would say to her daughter, "Now, remind me, who is Siggy?"

If you want to picture dementia imagine a cage around your brain. A cage that imprisons your thoughts, a cage that cuts off communication, that increasingly traps you within your own head. Memory, reasoning, communication are stripped from you. Your past is stripped from you. Biologically, it's the result of structural and chemical changes in the brain that lead to the death of brain tissue. Emotionally, for the family of those who are suffering, it leads to absence and it leads to loss, even when the person is physically present. The person they were is seen only in flashes. What is left, Magnusson records, is "empty eyes, grim mouth, vacant expression, stony face".

There was worse. Mamie's twin sister became the victim of Mamie's constant vicious sniping. Then there was Mamie's terror of any sort of change. Her inability to take in what was happening. And so a beloved daughter-in-law died too soon and there was no reaction. No words of grief or consolation. "I hate this disease," Magnusson writes at one point. "I hate it with a boiling fury. It has robbed you of the ability even to imagine what you cannot remember. It has stolen your empathy."

"The worst part of it," Magnusson says now of the decision to look after her mother, "is never being sure you're doing the right thing. We're not nurses. We're not doctors. Dementia in any case is something that few people know how to handle for best anyway. Seeing my mother's distress and agitation grow. There were many instances when we were able to help. There were some you can't and it's heartbreaking, it's utterly heartbreaking and there's maybe a bit of you that wishes that maybe you could hand it over and somebody would be doing it.

"But the positive side was by keeping her in her home, by surrounding her with people that she knew and loved, by continuing to sing with her, to make her laugh, we never actually lost her because that bit of her stayed connected."
What Magnusson and her sisters learned about dementia was that it doesn't rob a person of who they are. It just locks them in, locks them away. "And I think actually," Magnusson says, "it's been a false comfort in a way for many of us and indeed for society that when people get dementia [we think] they're actually so unaware that frankly you can set them aside because they're not really feeling anything anyway. They're not themselves. It was a painful revelation to discover how much my mother was aware right the way through of what she was losing, this sense of herself, her selfhood being inched away from her somehow. She felt it and was hugely frustrated about not being able to find the right words, of not being able to initiate actions."

One thing that helped was singing. Music is the last thing to go in us, Magnusson discovered. Mamie could be encouraged to sing, to grab hold of a lyric and pull herself along it. It's why her daughter has started a charity, Playlist For Life, to help encourage the use of music as a therapy for dementia sufferers.

But songs were momentary relief. The darkness kept closing in. One Christmas Eve Magnusson remembers coming into the house dressed in a short red dress and high heels and on a festive high only for her mother to not know who she was. "And more than that she didn't like this strange character."

By this point things were so confusing and alien for Mamie that this unfamiliar vision of her daughter was incomprehensible to her. "I can see that now, but at the time it was shocking. 'This is my mother. She doesn't know me, she doesn't love me and she'll never love me again. How can I bear this?'"

The next day Magnusson returned with no make-up and in her oldest clothes. "And she was sitting in front of the fire and I thought, 'I'm ready for anything here and I'm just going to be a nice stranger and that will be all and that's fine and I won't be hurt any more.' She just looked up and began to smile and stroke me and I said, 'Oh Mum, you quite like me today, don't you?' She sort of looked surprised and said, 'I love you.'"

If dementia care were a country," Magnusson writes in the book, "it would be the world's 18th largest economy." There are around 36.5m people in the world suffering from dementia, 800,000 in the UK. That number will grow as we live longer lives. The annual cost of care stands at around £400 billion a year - 1% of global GDP. In the UK that figure is more than £23bn, twice as much as cancer. Yet we spend much less on research.

"These are extraordinarily difficult things," Magnusson says when I raise these figures. "Everyone knows the constraints on the public purse and it's alarming when you look ahead and realise what the costs are. But that should be making us look for imaginative solutions. It's not just about finance, it's about how you think through how the money can be best used. It's about using the resources of families and building on these and finding ways of co-ordinating services better. And there's lots of thinking going on on that front.

"It's my generation and the one after that needs to look at this and find solutions instead of just being obsessed with being youthful for as long as possible which, of course, our culture is very good at. 'Let's see how young we can be for how long.'"

There is a moment in the book, when Mamie has been diagnosed with pneumonia, when Magnusson muses that drug development is "out of kilter". We can stop the lungs filling but not the brain eroding, she points out. "Better, perhaps, to face thinking about a time when the treatment might be allowed to stop."

Are you saying, Sally, we should let people slip away? "I think ... I'm not here to pontificate about the vast complexities. We all do a lot of pontificating, don't we, about other people's problems. They're vastly complex.

"All I'll say is that in the case of our own mother these questions came to mind and we wrestled with them and I think as a society we should wrestle with them."

She pauses and then says. "What this is is a plea. Don't be afraid of looking death in the eye. Don't be afraid of looking old age in the eye. Don't be afraid of looking at frail, vulnerable old people and realising that inside them is a beating heart and big emotions and a whole life's experience that could be woken up if you find the right way." But we are afraid, aren't we?

"We're terrified of our own mortality," she agrees. "I used to be terrified of death too. There's many people in my family that I have been with as they died and I've realised that death - the process of it - is not something to fear in itself. But death is another thing we've shoved away to happen in hospitals or somewhere else where it's sanitised. Let's just be unafraid."

Mamie Magnusson died in 2012, surrounded by her children, her words used up. Except … except in her daughter's book there is a letter. A letter written by Mamie to her in 1984, a few weeks before her daughter's wedding, a wedding her daughter was having second thoughts about, second thoughts that were bringing her out in a rash. It is a knowing, clever, thoughtful, uproariously funny letter. "You could," Mamie writes, "have put this step into marriage off. You could opt out altogether from this most challenging of all realms of living, with its heights of joy, depths of despair, its demands on resources of character and personality hardly suspected and maybe never needed in any other walk of life. Many people get through life without taking this step. Many would have loved to do it and never got the chance. You were lucky to meet the right man at the right time, and you made your decision."

Here is Mamie as she was, the wordsmith, the mother. "Without D Day looming ahead," she concludes, "without any choices to be made apart from the colour of the curtains, you can relax, cool down, be at peace. If the spots don't go away, then it must be the washing powder."

What did her daughter think when she read that letter 30 years ago? "I think my reaction was just what it always was when my mother wrote. 'Oh yeah Mum, you're right,'" Sally Magnusson says. "And I think I did change the washing powder too."

In the end words may be all we have. They may not be enough. But they're something. n

Where Our Memories Go, by Sally Magnusson is published by Two Roads, priced £16.99. The author will appear at Aye Write! book festival, which runs April 4 -12 in Glasgow. Visit ayewrite.com. See dementiascotland.org for advice and help.