The corpus callosum was found to turn off the right hemisphere while speaking

summary: The study confirms the role played by the corpus callosum in determining the linguistic aspects.

Source: HSE

A study by the HSE Center for Language and Brain confirmed the role of the corpus callosum in language tiling, and the distribution of language processing functions between the cerebral hemispheres.

The authors came up with an innovative language task for their study subjects and applied advanced neuroimaging methods to the data collected.

A paper about their findings has been published in Plus one.

The functional asymmetry between the cerebral hemispheres in performing higher-level cognitive functions is a major feature of the human brain. For example, the left hemisphere plays a leading role in language processing in most people. However, between 10% and 15% of humans also use the right hemisphere to varying degrees for the same task.

Traditionally, a right-hemisphere language bias has been explained by handedness, as it is found primarily in left-handed and unaccustomed individuals (using both hands equally). But recent research has shown a genetic difference in the way language is processed by left-handed people who don’t know anything about them.

In addition, some right-handed people also involve the right hemisphere in language functions.

These results prompted scientists to consider alternative explanations – in particular, by looking at the anatomy of the brain to find out why language functions are transmitted to the right hemisphere.

Researchers at the HSE Center for Language and the Brain hypothesized that the consistency of language may have something to do with the anatomy of the corpus callosum, the largest commissural pathway in the human brain that connects the two cerebral hemispheres.

The researchers asked 50 study participants to complete a sentence completion task. Subjects were asked to read aloud a visually rendered Russian sentence and complete it with an appropriate final word (eg, “Teper ministr podpisyvaet vazhnoe…” – “Now the minister is signing off on an important order…”).

At the same time, the participants’ brain activity was recorded using functional magnetic resonance imaging (fMRI). In addition, the volume of the corpus callosum was measured in each subject.

A comparison of fMRI data with measurements of the corpus callosum revealed that as the volume of the latter increased, less language function was observed in the right hemisphere.

It can be said that in language processing, the brain tends to use the resources of the left hemisphere efficiently and suppress, by means of the corpus callosum, any additional involvement of the right hemisphere. The larger the corpus callosum in a person, the less the right hemisphere is involved in language processing (and vice versa).

This result is consistent with the inhibitory model that the corpus callosum inhibits the action of one hemisphere while the other is involved in cognitive tasks.

This outline shows head and speech bubbles
Traditionally, a linguistic bias to the right hemisphere has been explained by handedness, as it is found primarily in left-handed and uncommon (using both hands equally) individuals. The image is in the public domain

The innovative study design and use of advanced neuroimaging made this conclusion possible.

“Usually, it is difficult to accurately measure the brain’s deviance in language processing, because typical speech tasks used in previous studies (such as naming pictures, choosing words that start with a specific letter or listening to speech) tend to cause activation in only some parts of the brain responsible for Language functions but not in others.

“Instead, we developed a unique fMRI speech task — sentence completion — that reliably activates all language regions of the brain,” says Olga Dragoi, director of the HSE Center for Language and the Brain.

It is important to add that the authors reconstructed the size and characteristics of the corpus callosum from the MRI data using an advanced technique in gravity science: constrained spherical dissociation (CSD).

This is more suitable than conventional diffusion tensor imaging for cross-fibre modeling in the smallest unit size, voxel (3D pixel), and thus more reliable.

About this language and neuroscience research news

author: Anastasia Lobanova
Source: HSE
Contact: Anastasia Lobanova – HSE
picture: The image is in the public domain

See also

This shows the synapses

Original search: open access.
Larger volumes of the subcallosal area ending in posterior lingual-related regions predict a stronger degree of lateral lingual dilatation: a study of organologyWritten by Victor Karbyshev et al. Plus one


Larger volumes of the subcallosal area ending in posterior lingual-related regions predict a stronger degree of lateral lingual dilatation: a study of organology

Lateral language is the most interesting feature of the functional asymmetry of cognitive functions.

At present, the genetic determinants of this trait are largely unknown, but there are efforts to find its anatomical correlates. In particular, a connection between the two hemispheres of the white sphere – the corpus callosum – has been proposed as such.

In this study, we aimed to find the relationship between the degree of language breadth and the measures of the corpus callosum subregions.

We applied an fMRI sentence completion task to measure the degree of language breadth in a cohort of healthy participants balanced for handedness.

We obtained the sizes and the exact structural characteristics of the sub-callous regions using two imaging techniques, Diffusion tensor imaging (DTI) And Restricted spherical dislocation (CSD).

DTI-based metrics analysis did not reveal any significant associations with language tiling. In contrast, CSD-based analysis revealed that sub-callous region volumes ending in posterior language-related core regions predict a stronger degree of lingual dilatation.

This result supports the specific inhibitory model implemented by projecting corpus callosum fibers in posterior language-related core regions in the language deviation score, with no relevant contribution from other corpus callosum subregions.

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