In his short story "Funes the Memorious," Jorge Luis Borges describes a man crippled by an inability to forget. He remembers every detail of his life, but he can't distinguish between the trivial and the important. He can't prioritize, he can't generalize. He is "virtually incapable of general, platonic ideas." Perhaps, as Borges concludes in his story, it is forgetting, not remembering, that is the essence of what makes us human. "To think," Borges writes, "is to forget."

To age is to forget, also. Roughly five million Americans have Alzheimer's disease, and even more suffer from mild cognitive impairment, or lesser degrees of memory loss. When asked to recall a list of 15 words read 20 minutes earlier, octogenarians in one large study recalled fewer than 60 percent, while the twentysomethings could remember close to 90 percent.

Not surprisingly, people have been searching a long time for chemicals that might halt that tide of forgetting. According to the Franciscan Bernardo de Lavinheta, writing in the early 1500s, "Artificial memory is twofold: the first part consists in medicines and poultices." The second part, of course, is the art of memory, which Lavinheta deemed both safer and more effective (since memory medicines can sometimes have the unfortunate side effect of "drying up the brain"). Today ginkgo biloba is sold as an over-the-counter supplement, or added to fruit smoothies and "smart" soft drinks, even without conclusive evidence that it either boosts memory—or dries up the brain.

Within the past decades, drug companies have elevated the search to brave new heights. Armed with a sophisticated understanding of memory's molecular underpinnings, they've sought to create new drugs that amplify the brain's natural capacity to remember. In recent years, at least three companies have been formed with the express purpose of developing memory drugs. One of those companies, Cortex Pharmaceuticals, is attempting to develop a class of molecules known as ampakines, which facilitate the transmission of the neurotransmitter glutamate. Glutamate is one of the primary excitatory chemicals passed across the synapses between neurons. By amplifying its effects, Cortex hopes to improve the brain's underlying ability to form and retrieve memories. When administered to middle-age rats, one ampakine was able to fully reverse their age-related decline in the cellular mechanism of memory.