I.

Introduction

Memory (psychology), faculty by which things from the past are brought to mind or retained there, or that which is so recalled. Memory is perhaps a person’s most distinctive characteristic. Our unique memories define who we are, a record of our personal past that also acts as a guide to our present and future. Memories endure: in our ninth decade we can recall episodes from our remote childhood. Every molecule and most of the cells in our body will have been replaced many millions of times, and yet our memories persist, and with them our sense of identity. This is why the loss of memory, by diseases such as Alzheimer’s or as a result of accidental brain damage, are so devastating.

Memory is so important to our lives that it is not surprising that its nature and mechanisms are a major theme of research in both psychology and neuroscience. Sixteen centuries ago, St Augustine devoted an entire chapter of his famous Confessions to puzzling over how it was that we could conjure up in our memories entire scenes and conversations, full of colour, scent, and sound, and yet our memory itself was spaceless, colourless, soundless. In the 17th century René Descartes proposed that memories were stored in the pineal gland in the brain by the bending of minute hairs with which the surface of the gland was studded, and the idea that memories are indeed in some way preserved in the brain in the form of some type of lasting change in structure or connections is still held by most researchers.

The modern scientific study of human memory began in the 19th century, when the losses of memory resulting from brain damage or alcoholism began to be catalogued. Normal human memory was studied experimentally by Hermann Ebbinghaus, who asked people to remember lists of words or nonsense syllables and noted that a large proportion were forgotten within the first hour or so, but that after that those items that remained persisted in memory—giving rise to the short-term, long-term distinction. The psychological study of memory has been built around the two poles of normal and abnormal ever since.