Flickering Lights: One-Shot Wonders versus the Network Model

Several bloggers have commented on Paul Bloom's Seed plaint about brain imaging studies receiving too much attention and a certain false credibility. (See the posts at Cognitive Daily , Mixing Memory and — in refutation — Small Gray Matters, as well as other citing blogs via Technorati or BlogPulse.) Bloom has a point: Both popular and science media show an outsized fondness for brain imaging studies, inspiring much work more diverting than informative. The most overhyped of these studies and stories suggest that in some busy brain area lies the locus of love, the center of empathy, or the key to fear of the new — as if a trinket dropped by Caesar along some road reveals the dynamics of Rome. Some skepticism is justified.

Thus Bloom's warning, as well as complaints from others that brain imaging amounts to a "new phrenology." Bloom's essay, in fact, fits into old arguments about how successfully we can localize the mind's doings; I wrote about this controversy over imaging and its historical roots early last year in Scientific American Mind.

But overlooked in Bloom's essay (and in much of the ongoing discussion of which it is part, including my SciAm Mind piece) is any distinction between two strains of fMRI studies that have been underway for some time. You need to recognize this distinction to really put a value on brain imaging studies, either individually or as a discipline.

One strain — the primary source of the complaints from Bloom and others — seeks simple correlations: here's a spot that lights up when we lie, see our children's faces, smell flowers, or confront a logical contradiction. These one-hit wonder studies can be done quickly and cheaply, so people do a lot of them, and they dominate the news releases on fMRI.

Another, more sophisticated line of inquiry gets less attention, partly because the study results appear less frequently (because the studies require more time, skill, and thought) and perhaps too because they're harder to explain in a few hundred words and a neat caption. These studies focus not on single-site activations but on defining the more complicated networks that drive mood, thought, and behavior. In the best of them, researchers take pains to coordinate the imaging research with research into genetic dynamics or other data that can serve as a check or corroboration on the imaging results. For example:

Joy Hirsch's lab at Columbia is looking into areas involving vision, attention, language, and chronic pain. A sweet example is Niewuwenhauis's and Yeung's "Neural mechanisms of attention and control," from Nature Neuroscience, which shows that the prefrontal cortex directs attention "by amplifying task-relevant invformation rather than inhibiting distracting stimuli". Good stuff.

A decade of careful imaging work defining depression networks led Emory's Helen Mayberg to believe that a previously overlooked brain area called Area 25 (aka the subgenual cingulate) plays a key role in depression. Her hypothesis was borne out dramatically when tiny pacemakers inserted in Area 25 in a dozen depression patients seemed to cure the depression of 8 of them. That surgical trial got wide press, including stories I wrote for
Scientific American Mind
and the
New York Times Magazine
. But all but a couple of the studies she did along the way were largely ignored.

Nikos Logothetis brings a masterly touch to his imaging studies while checking temptations to over-interpretation, overstatement, and other excesses. His review and theoretical essays on imaging have helped define the field's possibilities, limitations, and caveats. See his "Interpreting the BOLD Signal (pdf)"; his lab web page; or, (If you have a subscription to Nature, that journal's recent profile of Logothetis .

Finally, Marcus Raichle's lab at Washington University continues to do good work defining fundamental networks of attention. A typically rich paper in the Proceedings of the National Academy of Sciences describes how certain brain networks trade center stage — one dimming, as it were, as the other lights up — as the brain attends different tasks.

Studies of this caliber easily validate the promise of brain imaging. Rather than spotting trivial or questionable correlations, they identify pathways and physiological mechanisms underlying central dynamics of mood, consciousness, and cognition. Mayberg's work, for instance, reveals something vital about both the physiology and phenomenology of depression -- namely, that depression is not simply an absence or a lack but the instantiation of a network run amok. An active physiological dysfunction, a sort of neural equivalent of an overactive gland, underlies the what William James called the "active anguish" of deep depression. (For more on that, see my piece on her in the New York Times Magazine.)

Imaging may be producing some of the silliest papers these days. But it's also producing some of the most profound work in neuroscience.