A dominant hemisphere for handedness and language?

July 4, 2014, CNRS
Probability map of the brain regions activated in functional magnetic resonance imaging by a silent sentence production task in a group of 144 right-handed individuals. The color scale indicates the percentage of subjects with significant activation in this area during the task (green: 50%, blue: 65%, red: 80% or more). Note the high asymmetry of the map in favor of the left hemisphere. Credit: ©Groupe d’Imagerie Neurofonctionnelle (CNRS/CEA/Université de Bordeaux)

Through an innovative approach using a large psychometric and brain imaging database, researchers in the Groupe d'Imagerie Neurofonctionnelle (CNRS/CEA/Université de Bordeaux) have demonstrated that the location of language areas in the brain is independent of left- or right-handedness, except for a very small proportion of left-handed individuals whose right hemisphere is dominant for both manual work and language. This work was published in PLOS One on June 30, 2014.

Humans are the only species in which asymmetric is preponderant: 90% of people prefer to use their right hand and 10% their left hand. This motor behavior is "cross-lateralized": when using the right hand, the dominant left hemisphere is activated. Along with motor behavior, is one of the most lateralized functions of the body: the networks of brain areas controlling language are located asymmetrically in the brain's left or right hemisphere. Many studies have shown that the left hemisphere is dominant for language in 90% of cases, as it is for motor behavior.

Are the 10% of people who are left-handed and of those whose language is located in the brain's right hemisphere the same? Is the location of language areas in the brain correlated to handedness? To answer these questions, researchers from the Groupe d'Imagerie Neurofonctionnelle recruited a large sample of participants (297) including numerous left-handed subjects (153). Whereas most other studies only relate to right-handers (a majority of the population) these analyzed language lateralization for the first time in a large number of right- and left-handed individuals. The subjects in this sample were assessed using functional MRI while they performed language tests. Three types of language lateralization were then revealed from the images obtained (see figure 1): "typical" with a dominant (present in 88% of right-handers and 78% of left-handers), "ambilateral" without a clearly dominant hemisphere (present in 12% of right-handers and 15% of left-handers), and "strongly atypical" with a dominant right hemisphere (present only in 7% of left-handers). Statistical analysis of this distribution shows that concordance between the dominant hemisphere for handedness and that for language is random, except for a small fraction of the population (less than 1%) for whom the right hemisphere is dominant for both language and handedness.

These results show that knowing an individual's preferred handedness it is not sufficient to determine their dominant hemisphere for language. Researchers will now attempt to elucidate why only a small group of left-handers have a dominant for language, particularly by finding out whether there are genetic variants that might explain this phenomenon. These results also demonstrate that by contrast with a sample including a majority of right-handers, a sample enriched with left-handers composed from a large database shows variability factors in the brain structural and functional correlates: determining the sources of this variability in language lateralization may help to elucidate language pathologies.

Explore further: More left-handed men are born during the winter, study says

More information: Gaussian mixture modeling of hemispheric lateralization for language in a large sample of healthy individuals balanced for handedness. Bernard Mazoyer, Laure Zago, Gaël Jobard, Fabrice Crivello, Marc Joliot, Guy Perchey, Emmanuel Mellet, Laurent Petit, Nathalie Tzourio-Mazoyer. PLOS One, June 30, 2014.

Related Stories

More left-handed men are born during the winter, study says

July 3, 2014
Men born in November, December or January are more likely of being left-handed than during the rest of the year. While the genetic bases of handedness are still under debate, scientists at the Faculty of Psychology, University ...

Study finds emotion reversed in left-handers' brains

May 2, 2012
The way we use our hands may determine how emotions are organized in our brains, according to a recent study published in PLoS ONE by psychologists Geoffrey Brookshire and Daniel Casasanto of The New School for Social Research ...

Gorillas' right-handedness gives new clues to human language development

May 20, 2011
(PhysOrg.com) -- A new study that has identified a right-handed dominance in gorillas may also reveal how tool use led to language development in humans.

Recommended for you

New neurons in the adult brain are involved in sensory learning

February 23, 2018
Although we have known for several years that the adult brain can produce new neurons, many questions about the properties conferred by these adult-born neurons were left unanswered. What advantages could they offer that ...

Neuroscientists discover a brain signal that indicates whether speech has been understood

February 22, 2018
Neuroscientists from Trinity College Dublin and the University of Rochester have identified a specific brain signal associated with the conversion of speech into understanding. The signal is present when the listener has ...

Study in mice suggests personalized stem cell treatment may offer relief for multiple sclerosis

February 22, 2018
Scientists have shown in mice that skin cells re-programmed into brain stem cells, transplanted into the central nervous system, help reduce inflammation and may be able to help repair damage caused by multiple sclerosis ...

Nolan film 'Memento' reveals how the brain remembers and interprets events from clues

February 22, 2018
Key repeating moments in the film give viewers the information they need to understand the storyline. The scenes cause identical reactions in the viewer's brain. The results deepen our understanding of how the brain functions, ...

Biomarker, clues to possible therapy found in novel childhood neurogenetic disease

February 22, 2018
Researchers studying a rare genetic disorder that causes severe, progressive neurological problems in childhood have discovered insights into biological mechanisms that drive the disease, along with early clues that an amino ...

A look at the space between mouse brain cells

February 22, 2018
Between the brain's neurons and glial cells is a critical but understudied structure that's been called neuroscience's final frontier: the extracellular space. With a new imaging paradigm, scientists can now see into and ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.