I can never remember if Desert Island Discs is broadcast on Sunday and repeated on Friday, or the other way round. I’ve missed many rendezvous with interesting people because of this chronic memory lapse, and you can’t go to Listen Again because of copyright issues with the music. Still, thanks to a Post-it note last Friday, I managed to hear David Suchet.

It was fascinating to learn that the actor’s father, a surgeon, was disappointed with his middle son’s lack of academic purpose. That, age eight, he had been sent with his older brother John to a boarding school on the Kent coast, where they were forced to swim in the sea year round.

The image of the two little boys holding hands and walking into the freezing water singing You’ll Never Walk Alone was heartbreaking. But things got better. It was love at first sight when he met the actress Sheila Ferris in 1972 at the Belgrade Theatre in Coventry; on their first date, sitting on a bench at 3am, he burst into ‘When I fall in love, it will be forever’. And he did. They are still married and in love.

It’s impossible to separate David Suchet from Hercule Poirot, especially now when, thanks to the digital ITV3 channel, I watch Agatha Christie’s fastidious Belgian detective over and over. My memory is so rickety that I can never recall whodunnit, which may explain why I’m so fond of Desert Island Discs.

Despite claims that the lemony scent of madeleines is the greatest trigger of memory, I believe it is music that opens the rusty latches of the past. All week long, I’ve been singing When I Fall in Love to my cows, a mournful maternity whose calves are being weaned two fields away. My singing seems to comfort them, and it soothes me because I know all the words and I can also remember playing it over and over again, aged 16, when I first fell in love. I’m convinced that music is the live wire in the brain that functions longest, leaving us hymns and carols long after the names of lovers and rivers have vanished.

All the same, watching repeats of Poirot with the same wonderment of the first viewing led me to follow up David Suchet with Terry Pratchett’s remarkable account on BBC2 of his first year with Alzheimer’s, which, in a kind of zeitgeist of dementia, coincided with the interview in the Daily Telegraph with John Suchet, the protective older brother, who only days before had been wading into the sea as a little boy. Now he was revealing the heartache of watching his beloved wife, Bonnie, three years into her descent into Alzheimer’s. With trembling heart, I began to read a book I bought last summer by Sue Halpern called Can’t Remember What I Forgot.

First, the bad news. By 2025, dementia is expected to strike 34 million people globally. Half of all people who reach age 85 will exhibit some symptoms of the disease. The good news? The other half won’t. Watching Mr Pratchett’s search for strategies and delays was encouraging, because even with Alzheimer’s, his is a formidable brain. Miss Halpern’s assurance is for the ‘worried well’ living in the fog of pre-dementia. She explains that middle-age memory loss is perfectly normal, that as we get older we all suffer from ADHD, attention-deficit hypoactivity not hyper-activity. Our attention flickers, but it’s not that we forget. We simply don’t concentrate as well as we used to.

Neuro-scientists are developing drugs (called guanfacine) that revitalise concentration and memory in rats. Meanwhile, the scientists are firm on this. Exercise. Walk two miles a day. Briskly. Mice who take to the treadmill produce nice new neurons. Sedentary mice do not. And eat blueberries. They fight the atoms that damage brain tissue. I would add stick with Poirot and Nat King Cole. In a restless world like this is, love is ended before it’s begun.