How much can you trust your own memory?

"Remembering is a serious business," Charles Fernyhough warns. "For a journey into the past, you have to pick your moment."

It is this respect for his subject that makes Pieces of Light such an immense pleasure, as Fernyhough casts the emerging science of memory through the lens of his own recollections. The humiliating experience of potty training, for instance, helps him to illustrate the fragmentary, disordered nature of childhood memories before language indexes our past. Touching conversations with his late grandmother, meanwhile, colour his discussions of the ageing brain and the surprising longevity of narrative memories.

In the hands of a lesser writer, such reliance on personal experience could rapidly descend into self-indulgence and cliché, but Fernyhough - a psychologist and published novelist - remains restrained and lyrical throughout.

Like all good writing, the result shines new light on the reader's own life. As Fernyhough examines the way the brain continually rewrites our past, it is almost impossible not to question the accuracy of your recollections. Even the events that we recall with the most vivid sensory detail are not to be trusted. More than three decades of research has confirmed Salvador Dalí's assertion that "the difference between false memories and true ones is the same as for jewels - it is always the false ones that look the most real, the most brilliant". Disconcertingly, some of the chapters of our life story are simply borrowed from the experiences of our closest family.

On one level, such findings are deeply troubling - they have cast much doubt on the use of eyewitness testimonies in the courtroom, particularly when it concerns apparent cases of repressed abuse "recovered" through therapy.

But provided we tread carefully, Fernyhough sees no reason why this knowledge should deter us from journeying into our past. Our recollections "might be fictions", he says, "but they are our fictions, and we should treasure them".