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Flawed paper, ignores previous literature

Posted by Kounios on 20 Jul 2014 at 10:09 GMT

The popular media have promoted the idea that there are "right-brained" and "left-brained" people with particular cognitive styles. On the surface, this study seems to refute this idea. It uses functional magnetic resonance imaging (fMRI) data to suggest that there are no tendencies for some people to have more active right or left hemispheres. However, this study is both methodologically flawed and contradicted by a large research literature going back many years -- a research literature that this paper ignores. The popular idea of right-brained and left-brained individuals is somewhat exaggerated, but is nevertheless basically true. In particular, interested people are referred to two studies by Hagemann et al. done at the National Institutes of Health: a 2002 study in the Journal of Personality and Social Psychology and a 2005 study in Psycholophysiology. The 2002 paper reviews many relevant prior studies. Here are the URLs for these papers:


These Hagemann studies looked at the hemispheric asymmetry of resting-state electroencephalogram (EEG) alpha brainwaves. The rightward or leftward tendency that each person has is influenced by two factors, a stable trait and transient states. If EEGs were measured from each person during several sessions on different days. This caused the influence of transient states to cancel out, revealing a strong trait toward right-hemisphere or left-hemisphere activity. This trait was stable over time. It was also global: people who are right-brained or left-brained tend to be so at every part of the cerebral cortex that was measured. So the Hagemann et al. studies, which are a culmination of many studies by a number of investigators, show that many people tend toward being right-hemisphere types or left-hemisphere types, but that from moment to moment, environmental factors can cause functional hemispheric asymmetry to transiently shift to the other side. So being right- or left-brained is an average over time, but not a moment-to-moment rule.

So why does the current Nielsen et al. paper fail to find this effect? There are at least two possibilities. One is that the fMRI data they used were presumably recorded from each test subject during only one session. So the functional hemispheric asymmetry was probably diluted by fluctuating transient states. However, there is another feature of this study that was even more likely to have obscured their attempts to find such asymmetry: They looked for functional hemispheric asymmetry after statistically controlling for structural hemispheric asymmetry. In other words, when left/right physical differences between the two hemispheres were mathematically removed from the analysis, they found no difference in functional asymmetry, that is, no difference in brain activity. This procedure is, at best, questionable because functional differences between the hemispheres likely cause, or are caused by, the documented structural differences between the hemispheres. In other words, they found no right- or left-brained tendency after removing the likely cause of being right- or left-brained.

In sum, it is unfortunate that this study got so much attention because there is such a large, highly rigorous literature of studies that show that people do tend to be right or left brained. All this attention has set back the field by distracting people from this excellent previous research literature.

No competing interests declared.