The mysteries of human memory are deftly probed by Hilts, New York Times Washington correspondent on science and health policy (Scientific Temperaments, 1982, etc.). Hilts delves into the case of Henry M., who was left without a memory when drastic experimental brain surgery to relieve his epilepsy failed. Some 40 years after Henry's disastrous encounter with the surgeon's knife, researchers are still learning from his tragedy how the brain creates memories. Hilts came to know the gentle Henry as well as anyone can know a creature who lives only in the present moment. It's a fascinating account, made more so by Hilts's knack for finding concrete images, e.g., ""What . . . is now missing for Henry is the engine of memory which we use to catch the events of the world as they go by."" Although Hilts notes that describing the mind's mysteries has been largely left to scientists who cannot express well what they know and to poets who can express well but know little, his own writing achieves a gracious balance between science and literature. He shares painful personal memories, and he seeks out articulate scientists to help him explain the biology and chemistry of memory. In addition, Hilts traces a kind of history of memory--from its precursors in the responses of simple animals to marks made on bone by early humans to Homer's catalogs of ships and warriors to Proust's Remembrance of Things Past. His conclusion, that memory--the central trait of the human mind--is an act of construction, not of recording, and that memory's chief feature is its malleability, will afford little comfort to recovered memory therapists. Fans of Oliver Sacks will find much to savor here.