November 2010

Barbara J. King

features

The Dark Matter in our Heads: Carl Zimmer’s Brain Science

Give a group of undergraduates War and Peace and ask them to read the opening chapters. Instruct the students to tap a key whenever they become aware that their minds are wandering away from the text.

On average, that key will be tapped 5.4 times during 45 minutes of the students’ reading. Based on other research showing that people often remain unaware of their own mental drifting, the real sum of mind-wanderings almost certainly exceeds the reported number.

And there’s no use blaming Tolstoy. As Carl Zimmer shows in “The Neurobiology of Zoning Out,” one of 15 essays in his new book Brain Cuttings, the human brain veers off-task with surprising regularity. The experimental results on this point “are both humbling and shocking,” Zimmer writes. “Each of us has a magnificent hive of billions of neurons in our head, joined to each other by trillions of connections. And yet… we find it difficult to stay focused for more than a few minutes on even the easiest tasks.”

Zimmer describes fMRI research that pinpoints what areas of our brain activate during mind-wandering. Reviewing these areas’ names and functions, Zimmer concludes that during mind wandering “we may be able to think most deeply about the big picture.” We’ve all heard of the famous cases. For two weeks, a difficult proof gave the mathematician Poincare fits; only when he laid the problem aside, and began a bus journey, did the answer flash into his head.

My informants on Facebook tell me (in a highly unscientific poll) that this kind of experience is common. We’re not all grappling with hard math problems, to be sure; yet person after person told me that breakthrough ideas come to then only when they power down a challenging work task and walk the dog, ride a bicycle, hike, lay in bed and daydream, or take a shower.

Zimmer, then, invites us at times to absorb brain science by linking the data to some familiar experience in our lives. Other times, though, he makes us care about data that are fabulously unfamiliar. I felt tepid at best about the prospect of educating myself on glia cells when I began “The Brain’s Dark Matter.” But that’s the sneaky thing about Zimmer -- a few pages later, at his description of astrocytes (a type of glia cell), I was hooked.

“Named for their starlike rays, which reach out in all directions,” Zimmer notes, astrocytes are the most abundant of all brain cells and downright mysterious in their behavior:  “A single astrocyte can wrap its rays around more than a million synapses… [Astrocytes] have receptors that can snag a variety of neurotransmitters, which means that they may be able to eavesdrop on the biochemical chatter going on around them.”

The coolest thing about astrocytes, I learned, is that they respond to incoming signals with calcium waves, an unusual thing for a brain cell to do. Zimmer says why this matters, then concludes with a bang-on analogy between the glial cells in our heads and the dark matter in the universe: both are abundant, neither is well-understood.

Sometimes, the essays’ brevity brings on frustration. (The entry from Playboy, about the human-machine interface, is longer than the others.) In “Two Brains in One,” Zimmer reports what scientists have long known, that the brain-halves communicate through the corpus callosum. (When, in the neuro-anatomy lab, that tissue connection is severed, we get the brain cuttings of the book’s title).

New research asks how animals’ everyday actions reflect this hemispheric communication. “Perhaps paired regions take turns being dominant,” Zimmer suggests. “Dolphins use this strategy to sleep and swim at the same time: One hemisphere remains active for hours, then fades while the other takes over.”
And off Zimmer flits, in the next sentence, to consider bird brains.

But wait a minute; if dolphins swim and sleep simultaneously, then how does slow alternation of hemispheric dominance explain what’s going on? Here I missed Zimmer’s usual, crystal-clear step-by-step invitation to join the ranks of the scientifically savvy. (I just felt confused.)

In “The Googled Mind,” I was surprised to read that the extended-mind concept originated in 1998 with philosophers Andy Clark and David Chalmers. “The mind,” Zimmer explains, “appears to be adapted for reaching out from our heads and making the world, including our machines, an extension of itself.” Just so -- a recognition famously reached by the anthropologist Gregory Bateson, decades before Clark and Chalmers. (See Bateson’s Steps to an Ecology of Mind and his well-known example of a man felling a tree with an axe. The mind is not in the man, but in the tree-eye-brain-muscles-ax-stroke-tree system.)  

The sharp shock of a short essay’s single central idea suits the magazine format well, but why not push (even a little) beyond these constraints when clustering essays into a book? Unlike Zimmer’s many previous volumes, this one is available only as an e-book. That’s a fine new step to take, but e-publishing can, of course, embrace creativity as much as collecting.   

Its few lapses aside, I learned a tremendous amount from Brain Cuttings: what a “Halle Berry” neuron is; how querying about the workings of anesthesia may result from a science writer’s emergency appendectomy; that when a person encounters someone with an angry face, her facial muscles contract into angriness for a fleeting second, a sort of mimickry that may link to person-to-person empathy (and that may be shut down by Botox); and how it is that one brain disorder may cause “spells of passion” that evoke spontaneous orgasms.

Zimmer’s writing invites only the most welcome kind of mind-wandering, and brings a colorful zest to popular writing about the brain.

-- Tweet with Barbara @bjkingape