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Archive for 29/12/2010

Improving scan results

Yarkoni and others make a plea for collaboration and cumulative science in the mapping of brain functions, and in doing this they give much needed cautions to those of us that follow the images without any first-hand experience of a fMRI technology. I list here what they say are the short comings of individual studies.

  1. The studies are usually small, about 50-20 subjects, and the confidence thresholds are high, 0.001 or less. This limits the detection of activity to only very large effects and gives a misleadingly simple picture. Many effect are not seen in the small sample size or go unreported because they do not reach significance levels. Effects are likely to be far more widespread across the cortex rather than the highly localized picture we see.

  2. Even with very high confidence thresholds, there are many falsely positive results because of the extreme volume of results (the brain is big). Published false positive ‘lit spots’ in images are estimated at around 15%.

  3. Because of the expense on imaging studies, they are rarely actually duplicated by others. Instead near replications are done that give slightly different information. What is more it is difficult to replicate the exact location matches between studies even when the protocol is identical.

  4. One individual area of the brain can be activated by many tasks and so it is difficult to selectively pair an area to a function. The ‘area for X’ idea does not mean that if the area is active that therefore X is the current task. There is also the confusion of close and overlapping areas.

  5. The identification of networks, such as the ‘default’ and the ‘tasking’ ones, is hampered by the lack of agreement on how to describe both the brain areas and the cognitive tasks.

All these problems the authors feel could be reduced by sharing and integrating data. This requires common frameworks and formats, common databases and, of course, openness and cooperation. They detail these requirements.
Yarkoni, T., Poldrack, R., Van Essen, D., & Wager, T. (2010). Cognitive neuroscience 2.0: building a cumulative science of human brain function Trends in Cognitive Sciences, 14 (11), 489-496 DOI: 10.1016/j.tics.2010.08.004