I was on my way at last to the Magdalena, in an airport lounge at Bogotá, in transit from Madrid, waiting for a delayed flight to the Caribbean port of Barranquilla. It was early evening, and dark, fast-moving clouds gave a sad and restless look to this high, mountain-walled city, making me think of the teenage García Márquez, newly arrived here after his lifechanging first journey along the Magdalena and already pining for the perpetual summer of his coastal childhood. Exactly a year had passed since my encounter with the writer in Cartagena, in the course of which my own yearning for the Caribbean world had become at times unbearably intense. A disturbing deterioration in my mother''s dementia had led me to continually postpone my long-planned Magdalena quest. I had spent much of the year in a deeply introspective mood, searching for solutions for my mother, reflecting on her past, remembering my father, looking back to the distant time when I could never have imagined my parents'' gradual loss of dignity and independence, when I knew nothing of the pathology of mental decline, when I had thought of memory as a source of mystery and awe. My once high-flown notions of memory dated back to my adolescence, when I had been introduced to the multidisciplinary writings of a brilliant generation of cultural historians associated with London''s Warburg Institute. One day I discovered Frances Yates'' curious and compelling The Art of Memory, which traced the impact on the Middle Ages and Renaissance of an elaborate memory system evolved by the ancient Greeks. I was unable then to follow all of Yates'' exceptionally involved and subtle argument.

But I was taken by the idea of occult philosophers adapting for their own esoteric purposes a system that had originally been intended to have a purely practical application. I began to view memory as a key to an understanding of life''s secrets. I went on to spend much of my student years enclosed within the Warburg Institute, above whose entrance portal was inscribed the name of the ancient goddess of memory, Mnemosyne. The name became a daily reminder of memory as the central factor in our lives, the mother of the muses and the root of all knowledge. The sense of embarking on an intellectual adventure every time I entered the Institute was one that inspired in me early ambitions to become an academic. These ambitions faded during the many years I researched a doctoral thesis. The academic world I had once perceived in terms of vast intellectual and imaginative range came to appear restrictive and petty. The exposure of my PhD supervisor and principal referee as a former Russian spy forced me finally into a decision I had already half taken.

I took up a freelance life of writing and travelling. Combining the two activities meant I could explore academic subjects with the freedom and freshness I had so admired in the intellectual mentors of my schooldays. My early travels were driven by a love of art and architecture, and by a wish to visit as many countries as possible. But, with time, I began to concentrate on Spain and Latin America, and to be guided less by objects than by an interest in people and nature. I started also to indulge in the idea of travel as a metaphorical progression akin to walking through one of the philosophical landscape gardens that had obsessed me when I was younger. I remembered visiting with my parents an Italian garden in which water from an upper spring was directed downhill into an expanding labyrinth of channels and ponds leading to a giant basin emblematic of the sea into which all lives flow. The older I got the more I appreciated the role of travel as a stimulus to memories, and the way in which journeys even to new places were somehow always awakening memories of places seen in an ever-receding past. I was entering a phase of life in which my desire for travelling, far from being diminished, was acquiring a heightened urgency.

Witnessing the decline of my parents was like a lesson to me, calling up a Latin phrase as firmly embedded in my classically trained consciousness as the name Mnemosyne: carpe diem. By the time of my meeting with Gabriel García Márquez in January 2010, Colombia had become the main focus of my yearning for distant travel. Its echoes of old Spain satisfied my growing nostalgia, while the jubilance of its Caribbean world appeared to me now like a necessary affirmation of life. Though my mother''s continuing insistence on living alone made it impossible for me for the time being to consider lengthy journeys away from Europe, I allowed myself a brief return visit to Colombia in July. I had been invited there for the celebrations marking the country''s two hundred years of independence from Spain. These festivities coincided with the last days in power of President Álvaro Uribe, who was keen to be remembered as the man who brought stability to his country after two centuries of near-constant internal strife. As part of this public relations exercise, I was flown by helicopter to a model indigenous village in the coastal range of the Sierra Nevada de Santa Marta, where Uribe addressed the tribesmen with a talk about how this terrestrial paradise had now been rid of all the guerrillas, paramilitaries and drug traffickers who had once infested it. But the climax for me was climbing afterwards to an isolated bird sanctuary, where a break in a torrential rainstorm exposed at sunset an epic panorama of snow, jungle and sea.

I caught in that moment my first glimpse of the Magda - lena - as a faint glimmer of gold alongside the distant lights of Barranquilla. The next morning, flying back to Bogotá from the coast, I saw the river again, and was able to follow its dark grey band from the waterlogged flatlands of its estuary into the enormously long valley dividing the eastern and central ranges of the Andes. Then the plane swerved away and the view below me was obliterated by clouds. Hidden beneath their blanket, somewhere to the south, lay the Magdalena''s source. Though neither Márquez, nor Colombia''s early explorers, nor any of the travellers who had inspired my early interest in the river, had been to that place, I was resolved to do so myself. I envisaged the source as the ultimate goal of my forthcoming journey, as the mythical spring where Mnemosnye greeted travellers at the end of their lives. My mother''s condition deteriorated rapidly from July onwards, but my elder brother and I, perennial ditherers, were unsure as to what we should do about her. Numerous visits to doctors and hospitals did not solve this problem but at least gave me a better understanding of the physiology of memory.

Memory, instead of being the complement to imagination and the soul, was now explained as a neatly ordered mechanism involving millions of neurons being triggered from different parts of the brain to produce specific types of memories: shortterm, long-term, explicit, implicit, episodic and semantic. Whereas my father''s brain had been affected by protein abnormalities known as plaques and tangles, my mother''s, I was told, was displaying the symptoms of normal vascular deterioration. In the continuing absence of a cure for dementia and Alzheimer''s, a third of the world''s population is expected to end up like her by the middle of this century. Doctors assured my brother and I that we were doing exactly the right thing in allowing our independent-minded mother to continue staying in the house she had lived in for over fifty years. However, this did not lessen our sense of a crisis about to happen. We remained helpless onlookers watching her retreat into an ever more distorted version of her past. Italian by birth, my mother had lived mainly in London since marrying my Anglo-Irish father at the end of the Second World War. She had been an actress in a Sicilian touring company when they had first met, but had turned later into a housewife of exceptionally rigid habits.

For as long as I could remember she had maintained a pudding-bowl hairstyle, together with a weekly routine and timetable so unvarying that I knew, say, that our clothes would be washed on Monday and stuffed peppers served for supper on Sunday. She mistrusted spontaneity, even when it came to entertainment, which was limited to Saturday dinner parties, a Friday evening visit to the cinema or theatre, an extremely reduced television diet (mainly nature programmes, political debates and serializations of fictional classics) and, above all, reading. From five o''clock each afternoon she sat down in an armchair to read, her feet resting on a stool, her legs wrapped in a blanket. She began with the newspaper (always the Daily Telegraph) before moving on to a novel or memoir, or very occasionally a biography. There were certain books she read again and again, including Proust''s Remembrance of Times Past, which she knew almost by heart. Many of her other favourites were by Italian contemporaries of hers such as Leonardo Sciascia, Primo Levi and Natalia Ginzburg, whose writings seem to have helped keep alive the memory of her itinerant Italian upbringing. Though my mother ended up almost more fluent in English than in her native tongue, she continued to pepper her conversation with Italian phrases and family sayings of the kind that make up Natalia Ginzburg''s quirky memoir, Family Lexicon. She also shared with Ginzburg a family full of eccentric North Italian relatives and ancestors.

They would provide her with anecdotes to be brought up on every possible occasion. Both my parents were incorrigible tellers of stories about themselves and their families. My brother and I, and even our friends,.