'No Such Thing' as Left- or Right-Brained People - An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging

A while back I posted some information on the supposed right-brain/left-brain dominance of how one sees a spinning dancer (above). Now there is new evidence that suggests there is not any real right- or left-brain people or personality types.

Main points:

Dr. Jeff Anderson, lead author of the study, explains:

"It is absolutely true that some brain functions occur in one or the other side of the brain. Language tends to be on the left, attention more on the right.  

But people don't tend to have a stronger left- or right-sided brain network. It seems to be determined more, connection by connection."

Jared Nielsen, a graduate student in neuroscience at the University of Utah and one of the study authors, adds:

"If you have a connection that is strongly left-lateralized, it relates to other strongly lateralized connection only if both sets of connections have a brain region in common."

Interesting. Here is the summary from Medical News Today - below that is the abstract and citation for the original article (it's Open Access).

'No such thing' as left or right brained people

Written by Honor Whiteman | Medical News Today

19 Aug 2013

We have all heard references to people being a "left-brained" or "right-brained" thinker. But researchers from the University of Utah say their latest research shows this is a myth.

Previous studies over the years have suggested that we use one half of our brain more often than the other, playing a part in the type of personality we have. 

While the left side of the brain is usually associated with logical, analytical and detail-oriented behavior, the right side has been connected to creative, thoughtful and subjective thinking.

But a new study published in the journal PLOS ONE, suggests there is no evidence within brain imaging that proves some people are right-brained or left-brained.

The research team conducted a two-year study of 1,011 people who were part of the International Neuroimaging Data-Sharing Initiative (INDI), and who were between the ages of 7 and 29.

All participants had the functional lateralization of their brains measured. Functional lateralization means there are specific mental processes that take place in either the brain's left or right hemisphere.

Researchers have said the theory of "left-brained" or "right-brained" thinkers is nothing more than a myth

The scientists conducted the brain measurements using magnetic resonance imaging (MRI) analysis, which involved the participants lying in the scanner for 5 to 10 minutes while their "resting" brain measurements were taken. This allowed the researchers to correlate brain activity in one area of the brain and compare it with another.

The researchers then divided the brain into 7,000 regions and analyzed which regions of the brain showed more functional lateralization.

All connections in the brain were examined, and all possible combinations of the brain regions were correlated for each brain region that was left-lateralized or right-lateralized.

The results of the scan showed patterns indicating that a brain connection may be strongly left or right-lateralized. But they found no relationship that individuals "preferentially" used their left-brain network or right-brain more often.

Dr. Jeff Anderson, lead author of the study, explains:

"It is absolutely true that some brain functions occur in one or the other side of the brain. Language tends to be on the left, attention more on the right. 

But people don't tend to have a stronger left- or right-sided brain network. It seems to be determined more, connection by connection."

Jared Nielsen, a graduate student in neuroscience at the University of Utah and one of the study authors, adds:

"If you have a connection that is strongly left-lateralized, it relates to other strongly lateralized connection only if both sets of connections have a brain region in common."

Results of this study are groundbreaking, Nielsen says, as they may change the way people think about the "right-brain versus left-brain theory."

"Everyone should understand the personality types associated with the terminology 'left-brained' and 'right-brained' and how they relate to him or her personally," he says.

"However, we just do not see patterns where the whole left-brain network is more connected or the whole right-brain network is more connected in some people. It may be that personality types have nothing to do with one hemisphere being more active, stronger, or more connected."

Here is the abstract for the full article, available for free as an Open Access post at PLoS ONE:

Figure 5. Significant correlation of lateralized connections across subjects.

An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging

Jared A. Nielsen, Brandon A. Zielinski, Michael A. Ferguson, Janet E. Lainhart, Jeffrey S. Anderson

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.

Full Citation: 

Nielsen JA, Zielinski BA, Ferguson MA, Lainhart JE, Anderson JS. (2013, Aug 14). An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging. PLoS ONE, 8(8): e71275. doi: 10.1371/journal.pone.0071275