For nearly a century we’ve thought about the human brain almost solely in terms of its hundred billion neurons. Electrical signals pulse between millions of those long, slender cells, as though through the microprocessors in a computer, and bingo - we see; we think; we fall in love.
But only about 15 percent of all the cells in our brains are neurons. So how can we be sure that the microprocessor analogy is accurate? What about the other 85 percent?
A new book by R. Douglas Fields, a National Institute of Health neuroscientist, suggests that the other 85 percent - cells called glia that we have long dismissed as mere bubble wrap - may be far more important than we realized.
In “The Other Brain: From Dementia to Schizophrenia, How New Discoveries about the Brain Are Revolutionizing Medicine and Science,’’ Fields argues that glia represent a barely explored territory that should not be overlooked.
Labs around the country are finding that glial cells are involved in epilepsy, fetal brain development, mental illness, and even the generation of new neurons in adults. Others form a kind of super-aggressive commando unit that can tunnel through the snarls of dendrites and attack intruding organisms. Still others serve more like maniacal sidewalk sweepers, collecting and absorbing discarded potassium ions that are released by neurons when they fire.
All these roles, Fields believes, suggest the possibility that information travels not only through our neurons, but through a much vaster cellular network. “What would it mean to our current understanding of the mind and medicine,’’ he wonders, “if information flowed not only through neural circuits, but through glia as well?’’
Einstein’s brain, after all, contained as many neurons as yours or mine. But the numbers of Einstein’s glia? Off the charts.
Indeed, the glia that serve as guards, monitors, traffic cops, and overseers may knit together our entire nervous system. They might even learn, or sleep, or vary between men and women. As Fields puts it, “A revolution in our understanding of how the brain is built, how it functions, how it fails in mental illness and disease, and how it is repaired has been ignited with the recent exploration of these long-neglected brain cells.’’
In a less scientific new book, “The Hidden Brain: How Our Unconscious Minds Elect Presidents, Control Markets, Wage Wars, and Save Our Lives,’’ Shankar Vedantam, a Washington Post reporter, argues that another element of our brains has been neglected for too long: our unconscious minds. Vedantam argues that our “rational mind is unequal to the machinations’’ of this “hidden brain,’’ and that we “are being constantly fooled, tricked, and hoodwinked’’ by it.
“The Hidden Brain’’ presents the unconscious as a brutish, Stone Age set of adaptive instincts that makes rapid and often inaccurate summations about the world. Vedantam’s argument runs something like this: Our hidden brain’s priority is to quickly orient us in any situation and enable to us make rapid, lifesaving decisions. As a result, we often leap to bad judgments.
Consider the following experiment: Seventy-five New York University psychology students are given fairly extensive backgrounds on fictional vice presidents at a fictional company. Among the three executives one group is asked to evaluate is Andrea, described as “tough, yet understanding and concerned about others.’’ Another group considers James, who is also described as “tough, yet understanding and concerned about others.’’ Andrea is demanding but fair-minded; so is James. Indeed, the only difference between Andrea and James is that one has a woman’s name, and one has a man’s.
Then the students are asked which of these managers they’d like to work for. Four out of five say they’d prefer James.
Why? “There is a layer beneath the level of individual autonomy,’’ Vedantam writes, “where many of the really important decisions of life take place.’’ Using a wide array of anecdotal evidence, he goes on to argue that our hidden brain guides our investment decisions, our proclivities toward racism and sexism, our indifference to genocide, and even our willingness to become suicide bombers.
Fair enough, I suppose. It’s when Vedantam called these insights “extraordinary new discoveries’’ that my attention began to stray. What’s new about the idea that we’re not in conscious control of all our decisions? Certainly Freud, Shakespeare, and Plato had plenty to say about hidden motivations. Hasn’t all of advertising been built on that same idea?
Another problem inherent in Vedantam’s book is that he presents not so much a scientific argument as an anecdotal one. He’s most convincing when presenting selected studies such as the James and Andrea example, but when he presents profiles of people making decisions in real life, where there are many more contributing factors, the argument is not always as persuasive.
These reservations aside, “The Hidden Brain’’ remains compulsively readable. Vedantam is a gifted storyteller, and if his transit through pop behavioral psychology doesn’t revolutionize the way you think about your decisions, it will give you lots of interesting things to discuss with your friends.
“The Other Brain’’ offers an insightful, complex, and nuanced picture of the most interesting substance on earth: the matter inside our heads.
Anthony Doerr is the author of “The Shell Collector,’’ “About Grace,’’ and “Four Seasons in Rome.’’ 
