Losing It, By William Ian Miller

Would the author of Where Angels Fear to Tread have ventured upon butt-waxing? This stray, even idle thought surfaces while reading William Ian Miller's account of the shrinking brain and concomitant weakenings. He ranges widely but accords no space to EM Forster, who lived beyond 90 but, decades earlier, lamented the hair between his buttocks.

Despite gaining down below what he lost on top, Forster continued to write lucidly even if falling asleep at Britten's War Requiem and, on another occasion, humorously remedying the situation after failing to recognise Christopher Isherwood.

All of which is to wander from - or be stimulated by - Miller's study of the ageing brain. It grew, at 65, from his own preoccuption with senior moments - despite his ninetysomething mother continuing to swim a daily half mile and shame her juniors on the golf course. Still, vexingly, film-wise, Miller forgot the city - not Tangiers or Marrakech - in which police chief Claude Rains rounds up the usual suspects.

Miller's professorial subject is law, which for him means human nature, often echoed by his passion for the Icelandic Sagas, with equal measure accorded to the Bible. The rest of the "three-score years and ten" Psalm continues, "and if by reason of strength they be fourscore years, yet is their strength labour and sorrow; for it is soon cut off, and we fly away". By contrast, Miller's own prose is dry: a biscuit supporting the Stilton of his references and such aperçus as "it is next to impossible to cheat others of the small pleasures they achieve at your expense".

He is ready with Rochester's wonderful line, "and being good for nothing else, be wise". But, as he does Proust's last volume, he overlooks Matthew Arnold's poetic inversion of Browning's "Grow Old With Me" into the searing "Growing Old", when "we are frozen up within, and quite/ The phantom of ourselves,/ To hear the world applaud the hollow ghost/ Which blamed the living man".

Miller certainly shudders when glimpsing himself in a shop window, and notes that Alzheimer's patients, oblivious to their names on a nursing-home door, can find their way back by dint of a decades-old photograph thereupon. Looking back at his old articles, he boggles at references drawn upon without "the Google crutch".

Did Google sustain Losing It? If so, here is a full-throttle performance in which the Middle Ages are a solace for middle age. He embraces revenge, humilation, etymology, the Gettysburg Address - and Miller's grandmother who, at a young age, took to her bed, but drew a suitor into it, and, obviously enough, there yielded offspring.

If Miller's summaries of Sagas and Biblical stories cannot match the orginal, his book is the very reverse of the enfeebled Kingsley Amis endlessly typing "seagulls" – a departure so far from Verdi's great late flourishes. Which prompts another stray thought: instead of becoming a legend from another era, Virginia Woolf could easily have lived to sing along with Beatles songs.

That's hypothesis. Certainly, Miller's mother, not flying away, displayed amazing grace as he finished this book. It's not for me to spoil the story. Seek it out.