I do find the idea of left-brained and right-brained types to be unconvincing. When I first encountered the idea I was intrigued and tested the theory out in my family, friends and myself. What I found in my tiny sample was a lack of a pattern. I found people who were very logical and also very creative – which came more to the fore depended on what they were doing. There were people who showed the one strength more than the other, but still seemed to have some of the other when it was really needed. And of course, there were a few that were both fairly illogical and fairly uncreative – one might say they were not that bright. To me, the idea that there are two kinds of people is in the eye of the beholder. Scientists tend to be creative even though they must be logical; novelists tend to be logical even though they must be creative. Why are these cast as opposites?

Think about it, why would we have evolved, not an optimal archetype, but instead, a pair of sub-optimal archetypes. Why would we not be able to think logically when that was what would solve a problem, think creatively when that was what would work, or think both ways if that was required. The two hemispheres having different functions appears to be an ancient structural feature – maybe to do with a division of labour between immediate tasks and general lookout for danger. But the idea that the hemispheres can not work together at the same time on different cognitive tasks is not very believable.

The notion that there are “two types of people in the world, those that x and those that y”, seems to be an easy trap to fall into. So get your antenna tuned to notice when the world is being divided into opposites, types, domains, dimensions and the like, and be extra skeptical. The division may work well or it may be just pretty and simplistic.

Recent research (see citation below) has failed to find left-brained and right-brained people in a sample of more than a 1000 scans of neural connections in a resting state. There are networks that are restricted to one hemisphere (more or less), but the strength of these connections does not show the x-brain effect.

“we demonstrate that left- and right-lateralized networks are homogeneously stronger among a constellation of hubs in the left and right hemispheres, but that such connections do not result in a subject-specific global brain lateralization difference that favors one network over the other (i.e. left-brained or right-brained). Rather, lateralized brain networks appear to show local correlation across subjects with only weak changes from childhood into early adulthood and very small if any differences with gender.”

Here is the abstract:

Lateralized brain regions subserve functions such as language and visuospatial processing. It has been conjectured that individuals may be left-brain dominant or right-brain dominant based on personality and cognitive style, but neuroimaging data has not provided clear evidence whether such phenotypic differences in the strength of left-dominant or right-dominant networks exist. We evaluated whether strongly lateralized connections covaried within the same individuals. Data were analyzed from publicly available resting state scans for 1011 individuals between the ages of 7 and 29. For each subject, functional lateralization was measured for each pair of 7266 regions covering the gray matter at 5-mm resolution as a difference in correlation before and after inverting images across the midsagittal plane. The difference in gray matter density between homotopic coordinates was used as a regressor to reduce the effect of structural asymmetries on functional lateralization. Nine left- and 11 right-lateralized hubs were identified as peaks in the degree map from the graph of significantly lateralized connections. The left-lateralized hubs included regions from the default mode network (medial prefrontal cortex, posterior cingulate cortex, and temporoparietal junction) and language regions (e.g., Broca Area and Wernicke Area), whereas the right-lateralized hubs included regions from the attention control network (e.g., lateral intraparietal sulcus, anterior insula, area MT, and frontal eye fields). Left- and right-lateralized hubs formed two separable networks of mutually lateralized regions. Connections involving only left- or only right-lateralized hubs showed positive correlation across subjects, but only for connections sharing a node. Lateralization of brain connections appears to be a local rather than global property of brain networks, and our data are not consistent with a whole-brain phenotype of greater “left-brained” or greater “right-brained” network strength across individuals. Small increases in lateralization with age were seen, but no differences in gender were observed.

I assume that the left or right brain description of individuals will die a very slow death and years from now people will be using the labels – too bad, that’s life.

Nielsen JA, Zielinski BA, Ferguson MA, Lainhart JE, & Aderson JS (2013). An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging PLoS ONE, 8 (8) : 10.1371/journal.pone.0071275