No road, no trail can penetrate this forest. The long and delicate branches of its trees lie everywhere, choking space with their exuberant growth. No sunbeam can fly a path tortuous enough to navigate the narrow spaces between these entangled branches. All the trees of this dark forest grew from 100 billion seeds planted together. And, all in one day, every tree is destined to die.
Â Â Â This forest is majestic, but also comic and even tragic. It is all of these things. Indeed, sometimes I think it is everything. Every novel and every symphony, every cruel murder and every act of mercy, every love affair and every quarrel, every joke and every sorrowâ€‰â€"â€‰all these things come from the forest.Â
Â Â Â You may be surprised to hear that it fits in a container less than one foot in diameter. And that there are seven billion on this earth. You happen to be the caretaker of one, the forest that lives inside your skull. The trees of which I speak are those special cells called neurons. The mission of neuroscience is to explore their enchanted branchesâ€‰â€"â€‰to tame the jungle of the mind (see Figure 1).
Â Â Â Neuroscientists have eavesdropped on its sounds, the electrical signals inside the brain. They have revealed its fantastic shapes with meticulous drawings and photos of neurons. Their discoveries are amazing, but from just a few scattered trees, can we hope to comprehend the totality of the forest?
Â Â Â In the seventeenth century, the French philosopher and mathematician Blaise Pascal wrote about the vastness of the universe:
Â Â Â Â Â Â Â Â Â Let man contemplate Nature entire in her full and lofty majesty; let him put far from his sight the
Â Â Â Â Â Â Â Â Â lowly objects that surround him; let him regard that blazing light, placed like an eternal lamp toÂ
Â Â Â Â Â Â Â Â Â Â illuminate the world; let the earth appear to him but a point within the vast circuit which that star
Â Â Â Â Â Â Â Â Â describes; and let him marvel that this immense circumference is itself but a speck from theÂ
Â Â Â Â Â Â Â Â Â Â viewpoint of the stars that move in the firmament.
Shocked and humbled by these thoughts, he confessed that he was terrified by â€œthe eternal silence of these infinite spaces.â€ Pascal meditated upon outer space, but we need only turn our thoughts inward to feel his dread. Inside every one of our skulls lies an organ so vast in its complexity that it might as well be infinite.
Â Â Â As a neuroscientist myself, I have come to know firsthand Pascalâ€™s feeling of dread. I have also experienced embarrassment. Sometimes I speak to the public about the state of our field. After one such talk, I was pummeled with questions. What causes depression and schizophrenia? What is special about the brain of an Einstein or a Beethoven? How can my child learn to read better? As I failed to give satisfying answers, I could see faces fall. In my shame I finally apologized to the audience. â€œIâ€™m sorry,â€ I said. â€œYou thought Iâ€™m a professor because I know the answers. Actually Iâ€™m a professor because I know how much I donâ€™t know.â€
Â Â Â Studying an object as complex as the brain may seem almost futile. The brainâ€™s billions of neurons resemble trees of many species and come in many fantastic shapes. Only the most determined explorers can hope to capture a glimpse of this forestâ€™s interior, and even they see little, and see it poorly. Itâ€™s no wonder that the brain remains an enigma. My audience was curious about brains that malfunction or excel, but even the humdrum lacks explanation. Every day we recall the past, perceive the present, and imagine the future. How do our brains accomplish these feats? Itâ€™s safe to say that nobody really
Â Â Â Daunted by the brainâ€™s complexity, many neuroscientists have chosen to study animals with drastically fewer neurons than humans. The worm shown in Figure 2 lacks what weâ€™d call a brain. Its neurons are scattered throughout its body rather than centr