Functional Magnetic Resonance Imaging: The Perfect Imperfect Instrument: “Spatially, it is the gold standard, but poor temporal resolution has researchers looking for something better”:
“According to legend, functional neuroimaging can trace its roots to the stroke of noon on a day in the late 19th century, when Italian physiologist Angelo Mosso observed a sudden increase in brain pulsation in his test subject, Bertino the peasant. Using an elaborate contraption, Mosso had been measuring the pulsations coming from a soft spot in Bertino’s skull, the result of a head injury. Intrigued by the sudden pulsing, Mosso asked Bertino if the chiming of the local church bell had reminded him of his forgotten midday prayers. When Bertino said yes, his brain pulsated again. Then Mosso asked Bertino to multiply 8 by 12. Again, Bertino’s brain pulsated. Thus was borne the notion that blood flow in the brain is related to cognition.
That notion remains the basis of what some neuroscientists consider the most powerful in vivo brain imaging technology in use today, functional magnetic resonance imaging (fMRI). Since its emergence in 1992, fMRI has dominated the field of human brain mapping and has been featured in thousands of published papers–nearly an order of magnitude more than for any other functional imaging technique.” —The Scientist
FmH readers know of my love affair with this technology, given the psychiatrist’s voyeuristic romance with structure-function correlations in the brain — although more than one observer has referred to this, with all due irreverence, as neo-phrenology. I often point to dramatic fMRI findings here. This article is a good nontechnical overview of the technology, its strengths and limitations. There remains debate about what is actually being measured by fMRI scans, although the consensus is strong that it is an accurate reflection of brain activity during specific tasks.
The temporal resolution problem is not a technical limitation of the scanning methodology but a biological one — the changes in blood flow and metabolism that it visualizes in activated brain regions occur slowly, over 1-2 seconds, in response to task demands (far slower than the speed of thought, if you will). So it becomes impossible to segregate different stages in the brain’s response to a task demand. In many ways, the CNS remains a ‘black box’ with regard to the subtleties of mental events. Yet some think we are not nearing the limitations of the power of fMRI technology but rather near the beginning.
It may take a different kind of analysis of the data, the article suggests. One limitation of fMRI conclusions is that they depend heavily on the assumption that the brain is modular and that the activity of different regions during a mental event may be considered independently. In experimental studies using much more complex multivariate analysis to correlate changes between the voxels of scans, a crude kind of ‘mind reading’ even emerges:
…(T)rained observers first scanned volunteer subjects for several sessions while the volunteers looked at certain objects such as baskets, garden gnomes, and teapots. Cox and Savoy used a multivariate statistical approach–one designed to detect interactions among voxels–to identify brain patterns that corresponded to each object. When the volunteers’ brains were scanned again later, the observers used the patterns, which covered a large region of the cortex, to guess which objects the volunteers were looking at. Their guesses were up to 85% to 90% accurate. The study highlights the significance of coarse-grained neuronal patterns that extend over large areas, patterns that Cox and Savoy would not have found if they had relied on conventional fMRI statistical methodology.
Multivariate approaches to fMRI data are growing; they probably represent around 5% of the data analysis of current studies but will grow to predominate, some observers suggest, and with it will come a fundamental enhancement of our understanding of the interactions between various brain regions in mental activity.
Yet I have always worried about another assumption on which interpretation of the significance of fMRI data depends heavily. If you will allow me an apparent digression, this is a concern that first arose as I began to think about our romance with another technology, television, several decades ago, heavily influenced by Jerry Mander’s* estimable 1977 book Four Arguments for the Elimination of Television. Along with examinations of the way t.v. mediates experience, colonizes experience, and affects viewers’ physiology, one of Mander’s arguments, perhaps the most compelling for me as a student of human emotion and interaction, is how its inherent biases as a medium (despite anyone’s best intentions about what content it carries or what programming you choose to watch) shape our assumptions about human experience. Television is inherently better at conveying the coarse-grained aspects of emotion and interaction than the subtle; it delineates the exterior at the utter expense of the interior. As an example, because the histrionic outburst or the ugly grimace is resolved much more readily than the flicker of recognition or the momentary tightening of the corner of the mouth, it shapes the depiction of emotion at all levels including the scripting, direction and acting portrayal. More importantly, it directs the attention of consumers of the medium toward the dramatic and external aspects of experience and behavior and shapes their assumptions about what is most significant in human reality. Now you see where I am going; I worry that fMRI has a similar, inherent ‘flair for the dramatic’, and that the understanding of mental events derived from its data will always implicate regions with extensive, easily visualized changes rather than subtle flickers of difference. Gregory Bateson once defined information as a “difference that makes a difference.” We must be careful that the differences we see using fMRI are truly informative; our assumption that a region which undergoes a dramatic change in activation level during a mental event figures more centrally as a mental substrate of that event than another region with a more transient or subtle change in metabolic activity (perhaps because it was already highly active?) may be a questionable one.
*Mander, although less well known, deserves a place in the pantheon of cultural critics alongside, for example, the recently deceased, celebrated, Neil Postman. More recently, Curtis White in his crucial 2002 book The Middle Mind: Why Americans Don’t Think for Themselves, has done Mander one better. While Four Arguments showed why and how the medium of television stops people from the thinking that would interfere with their political obedience and consumption, White argues that this is the effect of both high- and lowbrow popular culture as a whole.
