Wednesday, May 1, 2013

What Good is Neuroimaging?

If there is one absolute in this universe, it is that people want more stuff. Given the choice between stuff and nothing, people will choose stuff, nine times out of ten. Therefore, as science is a business as well as an intellectual pursuit, any scientist would be well-advised to take a step back once in a while and consider whether his work makes the public feel as though that they are getting more stuff. This gets back to the divide between basic research and translational research: basic research being done more for its own sake, and to just figure stuff out; and translational research, which attempts to bridge basic scientific findings and transform them into improved technologies or therapies.

A recent article in the Journal of Cognitive Neuroscience (Moran & Zaki, 2013) addresses these very issues, stating that neuroimaging has reached a critical mass of exploratory findings through brain mapping, but in order to advance will have to take a more theoretically rigorous approach. In the good old days, it was interesting to do basic exploratory analyses to examine the functional role of large chunks of cortical real estate, such as the visual cortex, auditory cortex, and some subcortical structures. However, the authors maintain that most new exploratory brain analyses - i.e., those that simply want to find out what brain region is responsive to a certain task or a certain stimulus - are rapidly entering the far end of diminishing returns. What is needed, rather, is experiments that can adjudicate between competing theories of brain function, using forward inference to distinguish between alternative hypotheses, instead of reverse inference, which reasons that because a particular region shows more activity than normal, then a particular process must be involved (cf. Poldrack, 2006).

However, even with reverse inference, some assumptions can be made about a cognitive state. For example, with large-scale databases such as Neurosynth, one can quickly see how many studies claim that a given region is involved in a particular cognitive process. This lends more credibility to reverse inference claims that dovetail with evidence from the majority of studies, as opposed to selecting a single study that claimed to have found evidence of a cognitive process associated with a certain area, as this may be more susceptible to a false positive.

For practical uses, however, neuroimaging - and FMRI in particular - has been able to make predictions about behavior based on brain activity. For example, in a growing body of decision-making research, increased activity in the anterior insula predicted better choices in a risky decision-making task (Krawitz et al, 2010), and within a group of smokers shown anti-tobacco ads, dorso-medial prefrontal cortex activity predicted levels of a nicotine metabolite at a later follow-up (Wang et al, 2013). This seems to be a profitable avenue of neuroimaging research, as neural activity can provide more information about effective treatment programs, from drug PSAs to psychological therapies, above and beyond behavioral measures.

In light of all this, the evidence suggests that, although brain mapping for its own sake will continue to be popular, the higher-impact work appears to be shifting more emphatically in the direction of translational research. The human desire for stuff will always trump the human desire of curiosity, and the researcher would be wise to pay heed to this, lest he be swallowed up in darkness.

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