Senin, 21 Oktober 2013

Brain Imaging: What Good Is It?

You've no doubt seen those colorful pictures of the brain, with different sections of the brain colored yellow, red, green, and blue—a rainbow pattern of colors spread out across the brain. These images are generated by a brain imaging technology called "functional magnetic resonance imaging" or fMRI for short. fMRI can detect the relative degree of brain activity in a very small region of the brain, approximately 3 millimeters cubed. These little imaginary cubes are called "voxels"; and then, using some expensive and fancy technology, researchers can measure the brain activity in each voxel while you're engaged in a specific mental task. To communicate the results, each of the voxels is assigned a color based on how much the neurons inside it are firing. Scientists, journalists, and trade book authors are really excited about this technology, because it seems to give us a window into what is really going on when we're thinking. National funding agencies have been granting lots of money to this sort of research (and it's not cheap, because it requires expensive machines that are often located inside the medical school, because they're also used for clinical diagnoses).
So what good is it? More and more scholars are asking this question, and we're seeing a growing backlash. Knowledgeable scholars have been arguing that we haven't learned much from this expensive brain imaging. Adam Gopnik, writing in The New Yorker magazine, recently reviewed three new books that all argue "that brain science promises much and delivers little." The books are A skeptic's Guide to the mind, by Robert A. Burton; Brainwashed: The Seductive Appeal of Mindless Neuro-Science, by Sally Satel and Scott O. Lilienfeld; and Neuro: The New Brain Sciences and the Management of the Mind, by a pair of cognitive scientists, Nikolas Rose and Joelle M. Abi-Rached. (Not included in this review is the 2011 book Neuromania: On the Limits of Brain Science, by Paolo Legrenzi, Carlo Umilta, and Frances Anderson.) As Professor Roger Carpenter writes, in a letter supporting Gopnik's review, this "is indeed neo-phrenology, and, intellectually, represents a regression to the nineteenth century." (Sep. 23, 2013, pp. 12-14)
In 2011, I published a scientific article titled "The cognitive neuroscience of creativity,"* and I came to the same conclusion about the limits of brain imaging. The first challenge is that you have to learn a lot of technical detail to really understand how little information the technology provides. For example, in my article I reported that fMRI, which indirectly measures neuronal activity by measuring blood flow to each voxel, is in fact only measuring changes in blood flow above a baseline state of 1 percent to 3 percent. That means that even when your neurons are firing like crazy, you won't see more than a 3 percent increase above a baseline state (i.e., sleeping or daydreaming). Second, when neurons start firing, the blood flow doesn't increase until 4 to 6 seconds later. Third, when neurons become more active, they draw in more blood, but blood flow also increases over a larger area that extends to a few millimeters distant, where there may not be any increase in neuronal activity. 
Fourth, different people's brains operate in different ways—not everyone's brain responds to a given task in exactly the same way. Even for a single person, their brain responds differently to the same task on each occurrence of the task. So researchers have everyone do the task tens or hundreds of times, and then they take a statistical average across all of the tasks. And after that, they average across everyone's brain. So those colorful pictures you are seeing represent an average—and it doesn't mean that every person, every time, displays exactly that activation pattern.
And finally, the colorful pictures hide a very important fact: The entire brain is active pretty much all of the time. Neurons are always firing, at least a few times every second. The brain is a complex system, and every cognitive activity is widely distributed across the neocortex. If you showed those pictures in a magazine, it would look like a jumbled mess. So researchers do what's called paired image subtraction—they get the average brain activity in one task, and then they get another average, of brain activity in some comparison baseline task, and they subtract out the activity of the baseline task.
Are you confused yet? I said there were a lot of technical details. (And the above is a highly simplified version.) But all this led me to draw the following conclusions in my 2011 article:
1. For the most part, brain imaging has discovered facts that were already known from classic experimental cognitive psychology. We have no breakthrough surprises; no 1970s experimental findings have been overturned.
2. All thought involves many regions of the brain. There is no such thing as "the brain location for creativity" or anything else.
3. You can't use brain imaging to make claims about causation, such as "activation in this part of the brain caused you to have a creative insight," because the activated areas might not play a critical role in performing the task; they might be "listening" or monitoring some other brain area that is actually responsible.
4. Because the brain imaging results are always averaged over many trials and many subjects, it is incorrect to interpret the studies as showing that "creativity is located in the anterior cingulate cortex" (or wherever).
5. Higher cognitive functions, like creativity, are complex and involve many parts of the brain simultaneously. They can't be reduced to one small location in the brain. And when you think about it, that's just common sense.
Perhaps new technologies will emerge in the future that can address some of these issues. But whatever new brain imaging technology emerges, these five points will still apply. I'll certainly keep following this research, and if I see some exciting new finding about creativity and the brain, you'll read it here!

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