Left Brain, Right Brain: A Conversation on Lateralization and Handedness
Dr. Sebastian Ocklenburg explains what brain asymmetry is (and is not), why handedness gets misread, and how researchers actually measure “left” vs “right” lateralization.
Meet Dr. Sebastian Ocklenburg — psychologist and professor for research methods in psychology at MSH Medical School Hamburg in Germany.
Dr. Ocklenburg’s research focuses on brain lateralization (hemispheric asymmetries), including handedness and language lateralization. He has written widely for public audiences about what brain asymmetry does and does not mean (including through his Psychology Today blog, The Asymmetric Brain).
Across his academic work, Dr. Ocklenburg has investigated how asymmetries develop and how they relate to factors such as genetics/epigenetics, stress, and neurophysiology, using methods including neuroimaging and electrophysiology.
He has received several early-career recognitions, including the Heinz-Heckhausen Young Investigator Award from the German Psychological Society for his dissertation (2012) and the Brain Products Young Scientist/Young Investigator Award (2019), both of which were awarded in recognition of his work on language lateralization.
In this NeuroKnow Conversations issue, Dr. Ocklenburg breaks down what scientists mean by “left-lateralized” and “right-lateralized,” why handedness gets misunderstood online, and how students can view brain differences without turning them into labels.
Q: ‘Left brain versus right brain’ is a common idea. In accurate neuroscience terms, what is brain lateralization, and what is the most common misunderstanding people have about it?
Prof. Dr. Ocklenburg: Brain lateralization refers to structural and functional left-right differences in the brain. A common misunderstanding is that there are left-brained people who use intellect to process information and right-brained people that are more emotional. This is incorrect, all people use both hemispheres. Also, lateralization is typically relative. A brain function like language is controlled by a complex network of brain areas. For some functions, these networks rely more heavily on areas on one side of the brain, but the other side is used, too.
“… all people use both hemispheres.”
Q: Handedness can often be treated as a personality label. What can handedness realistically suggest about brain organization, and what can it not inform us?
Prof. Dr. Ocklenburg: Handedness is not a personality label, but a motor preference. A large scale study found the regarding brain organization left- and right-handers show statistically significant differences in structural asymmetries of the precentral cortex, which contains part of the brain's motor network. Further differences were found in the fusiform cortex, the anterior insula, and the anterior middle cingulate cortex. These areas are relevant for emotions and face perception, cognitive systems that are strongly lateralized.
Q: People often assume handedness perfectly predicts where language “lives” in the brain. What does research actually support about the handedness-language lateralization relationship, and what remains uncertain?
Prof. Dr. Ocklenburg: Handedness and the language-dominant hemisphere are linked, but handedness does not predict language lateralization perfectly. For right-handers, about 95% show left-hemispheric language dominance, so the association is very strong. For left-handers, 25% show right-hemisperic language dominance, but 75% still show left-hemispheric language dominance. Thus, both left- and right-handers are more likely to have left-hemispheric language dominance, the percentage is just substantially lower in left-handers.
“Handedness and the language-dominant hemisphere are linked, but … not perfectly.”
Q: When do brain asymmetries begin to develop during development, and are there related changes during adolescence that are interesting yet easily overinterpretable?
Prof. Dr. Ocklenburg: They begin to develop long before birth, and these prenatal asymmetries are predicting later asymmetries pretty well, although not perfectly. Typically, brain asymmetries are less developed during early childhood and get stronger over adolescence, but the patterns of individual brain areas are complex.
Q: When scientists say something is “left-lateralized” or “right-lateralized,” how is that usually measured? What commonly leads individuals to overinterpret these results?
Prof. Dr. Ocklenburg: It could for example mean that if we put a volunteer into an MRI scanner and look at brain activations while they do something (like listening to speech), left-lateralized would mean that there are statistically more active brain areas in the left hemisphere than in the right. It does, however, not mean nothing is happening in the right side of the brain. The overinterpretation of brain imaging figures often happens because they show statistical maps of activations that go over a certain threshold, not all activity. This then makes the impression nothing is happening on the other side, which is not correct.
Q: Outside the textbook, where does asymmetry research genuinely assist us in thinking more clearly without overlabelling others? If you had to choose one key insight about brain asymmetry that is most important or most misunderstood, what would it be and why?
Prof. Dr. Ocklenburg: The fact that the brain has two sides is its most visible organizational feature. Understanding that functions are distributed asymmetrically in the brain and the fact that this is not the same for everybody (e.g., 25% of left-handers are right language dominant) has huge implications for treatment of neurological and psychiatric disorders with the neurostimulation techniques like TMS.
Q: If a student wanted to explore this field seriously, what skills would you recommend building early (especially around research methods and statistics), and what kinds of experiences would develop a strong base?
Prof. Dr. Ocklenburg: The field has a rich history and reading up on it in detail helps understanding where current directions of research come from. Reading the journal “Laterality” makes a lot of sense! In general, knowledge of one or more neuroscientific techniques like fMRI would be a good start. Also, knowing your way around a statistics software like R or JASP is important. Last but not least I would recommend visiting the biannual North Sea Laterality Meeting!
Thank you, Prof. Dr. Ocklenburg!
Links:
https://www.psychologytoday.com/us/blog/the-asymmetric-brain
https://www.sciencedirect.com/book/monograph/9780323997379/the-lateralized-brain
Follow Dr. Ocklenburg on Bluesky (@ocklenburg.bsky.social) and X (@ocklenBLOG)
Niceee, to be doctor 👩⚕️ 😃