Understand lateralization without labeling people
If you want to understand what the brain’s two hemispheres do, start with a useful distinction: some brain functions are lateralized, meaning they rely more on one side than the other in particular ways. That does not mean people fall into “left-brained” logical types and “right-brained” creative types. The best-known brain-imaging test of that personality claim found no evidence for a general left- or right-dominant brain network across individuals. This guide explains what lateralization means, what the evidence can and cannot tell us, and how to assess claims about hemispheric differences.
What does hemispheric lateralization mean?
The brain’s left and right hemispheres are not identical copies. In neuroscience, hemispheric lateralization refers to a function or pattern of brain activity being more strongly associated with one hemisphere than the other. “More strongly associated” matters: it describes a relative bias, not an exclusive assignment in which one side works alone.
Language and visuospatial processing are examples of functions that can show lateralized patterns. The University of Utah researchers who conducted a large imaging study identified left-lateralized hubs in regions associated with language and the default mode network, and right-lateralized hubs in regions associated with attention control. Those findings illustrate that lateralization can vary by brain region and network. They do not establish that every language or spatial task belongs wholly to one side.
The everyday phrase “left brain versus right brain” often turns this specific idea into a broad personality story: analytical people supposedly favor the left, while imaginative people favor the right. That leap changes the question. A difference in how a particular connection or function is distributed is not evidence that one person’s whole brain is globally dominated by a hemisphere.
What did the PLOS ONE study find?
In a 2013 peer-reviewed study in PLOS ONE, Jared Nielsen and colleagues analyzed resting-state brain scans from 1,011 people aged 7 to 29. The researchers measured functional lateralization across pairs of brain regions and asked whether strongly left-lateralized connections tended to cluster together within individuals, and whether the same was true for right-lateralized connections.
They identified left- and right-lateralized hubs, but the pattern of lateralization appeared local rather than global. In other words, strongly lateralized connections were not evidence of an individual-wide left-dominant or right-dominant network. The authors concluded that their results did not support the idea of a general “left-brained” or “right-brained” phenotype. The University of Utah’s educational summary of the research makes the same central point: the study found no imaging evidence for the popular personality categories.
The scope of the result matters. The study tested a specific brain-network hypothesis using resting-state imaging. It did not measure every human ability, explain every form of hemispheric specialization, or show that hemispheres never differ. Its finding challenges the claim that individuals can be sorted into whole-brain personality types based on hemisphere dominance; it does not erase the more focused scientific study of lateralization.
Why doesn’t lateralization create personality types?
A common error is to move from “some functions show a hemispheric bias” to “a person is governed by one hemisphere.” Those statements are not equivalent. A pattern seen in some regions or connections cannot, by itself, establish a stable personality category that applies across reasoning, creativity, communication and everyday behavior.
The PLOS ONE study addressed this by
testing whether lateralized connections covaried across the same individuals in a way that would indicate a broad left- or right-dominant network. Its findings did not show that global pattern. The authors instead described lateralization as a local property of brain networks. This is a more precise way to talk about the evidence: ask which function, which regions or connections, and under what conditions, rather than assigning a person an all-purpose hemisphere label.
The study also used resting-state scans, so its results are about patterns measured while participants were not performing a specific reading, drawing or reasoning task. They should not be stretched into claims that a particular activity activates only one hemisphere. The University of Utah summary is useful for correcting the personality myth, while the original paper gives the methods and limits needed to interpret the finding carefully.
A reading-and-sketching example
Imagine reading a short description of a room and then sketching its layout. Reading the passage involves interpreting written words and following their meaning. Sketching requires turning that understanding into a spatial arrangement on paper. It may be tempting to label the first step “left-brain” and the second “right-brain,” then conclude that the activity switches from one hemisphere to the other.
That conclusion goes beyond what the example can show. Reading and drawing are complex tasks; their names do not tell us which networks are active in an individual. The fact that some language and visuospatial functions can be lateralized does not prove that each whole task belongs to just one side, or that a person’s success at either task reveals a dominant-brain personality. The defensible takeaway is narrower: different components of an activity may draw on different processes, and researchers need to measure brain activity to investigate their lateralization. This example is a way to practice careful interpretation, not a claim about a scan or a measured task result.
A checklist for interpreting brain-hemisphere claims
When you encounter a claim about left- or right-brain functioning, ask:
If a source jumps from a specific observation to a sweeping label without showing that link, treat the label as an interpretation, not as a demonstrated fact.
Conclusion
Hemispheric lateralization is a real, focused concept: some functions and brain networks can show stronger associations with one side. But the existence of lateralized patterns does not justify classifying people as globally left-brained or right-brained personalities. Nielsen and colleagues’ analysis of 1,011 resting-state scans found no evidence for that whole-brain phenotype, while also identifying local lateralized networks. When evaluating a hemisphere claim, keep the measured function, method and scope in view. That approach preserves what neuroscience can tell us without asking a specific brain difference to explain a whole person.
Sources and scope
Original reading-and-sketching example and source checklist keep task observations distinct from personality labels. The listed sources support the study descriptions; examples and exercises are original editorial applications.