Why the left hemisphere of the brain understands language better than the right

July 12, 2018

Nerve cells in the brain region planum temporale have more synapses in the left hemisphere than in the right hemisphere - which is vital for rapid processing of auditory speech, according to the report published by researchers from Ruhr-Universität Bochum and Technische Universität Dresden in the journal Science Advances. There has already been ample evidence of left hemisphere language dominance; however, the underlying processes on the neuroanatomical level had not yet been fully understood.

A new form of magnetic resonance imaging (MRI) in combination with electroencephalography (EEG) measurements has made it possible to bundle insights into the microstructure of planum temporale with the speed of auditory speech processing. The team headed by Dr Sebastian Ocklenburg, Patrick Friedrich, Christoph Fraenz, Prof Dr Dr h. c. Onur Güntürkün and Dr Erhan Genç outlines their findings in an article published in the scientific journal Science Advances from July 11, 2018.

Left hemisphere language dominance

Using a simple experiment, researchers can demonstrate just how superior the left hemisphere is when it comes to the processing of auditory speech: when playing two different syllables - for example "Da" and "Ba" - to a person's left and right ear via headphones, most people will state that they only heard the syllable in the right ear. The reason: language that is perceived via the right ear is processed in the left hemisphere. When brainwaves are measured using EEG, it emerges that the left hemisphere processes auditory speech information more rapidly.

"Researchers have long determined that a brain region that is crucial for the processing of auditory speech, i.e. planum temporale, is frequently larger in the left hemisphere than in the right one," says Sebastian Ocklenburg from the biopsychology research unit in Bochum. In the brains of deceased individuals who had donated their bodies to science, Frankfurt-based researchers later discovered that the nerve cells in the left planum temporale have a larger number of neuronal synapses than those in the right hemisphere.

New measurement method facilitates hitherto impossible insights

"However, it had previously not been understood if that asymmetrical microstructure is the decisive factor for the superiority of the left hemisphere when it comes to the processing of auditory speech," explains Erhan Genç, likewise a member of the biopsychology research unit. Since a method for counting the number of neural synapses in living humans had not existed until very recently, that number could not be conclusively linked to the performance of auditory speech processing. The researchers have now closed this gap with the aid of so-called neurite orientation dispersion and density imaging.

By deploying this highly specific MRI technology, the bio-psychologists measured the density and spatial arrangement of planum temporale neurites in almost one hundred test participants. At the same time, they used EEG measurements to analyse the processing speed of auditory speech information in both the left and the right hemispheres in the same individuals.

Higher speed thanks to more neurites

The result: test participants who were capable of processing auditory speech in the left hemisphere at a high speed possessed an extraordinarily high number of densely packed neurites in the left planum temporale. "It is because of this microstructure that processing of auditory speech is faster in the left hemisphere; those individuals are presumably also able to decode what they hear at higher temporal precision," concludes Ocklenburg. "Higher connectivity density thus appears to be a crucial component for the linguistic superiority of our left hemisphere," adds Genç.
-end-


Ruhr-University Bochum

Related Nerve Cells Articles from Brightsurf:

Nerve cells let others "listen in"
How many ''listeners'' a nerve cell has in the brain is strictly regulated.

Nerve cells with energy saving program
Thanks to a metabolic adjustment, the cells can remain functional despite damage to the mitochondria.

Why developing nerve cells can take a wrong turn
Loss of ubiquitin-conjugating enzyme leads to impediment in growth of nerve cells / Link found between cellular machineries of protein degradation and regulation of the epigenetic landscape in human embryonic stem cells

Unique fingerprint: What makes nerve cells unmistakable?
Protein variations that result from the process of alternative splicing control the identity and function of nerve cells in the brain.

Ragweed compounds could protect nerve cells from Alzheimer's
As spring arrives in the northern hemisphere, many people are cursing ragweed, a primary culprit in seasonal allergies.

Fooling nerve cells into acting normal
In a new study, scientists at the University of Missouri have discovered that a neuron's own electrical signal, or voltage, can indicate whether the neuron is functioning normally.

How nerve cells control misfolded proteins
Researchers have identified a protein complex that marks misfolded proteins, stops them from interacting with other proteins in the cell and directs them towards disposal.

The development of brain stem cells into new nerve cells and why this can lead to cancer
Stem cells are true Jacks-of-all-trades of our bodies, as they can turn into the many different cell types of all organs.

Research confirms nerve cells made from skin cells are a valid lab model for studying disease
Researchers from the Salk Institute, along with collaborators at Stanford University and Baylor College of Medicine, have shown that cells from mice that have been induced to grow into nerve cells using a previously published method have molecular signatures matching neurons that developed naturally in the brain.

Bees can count with just four nerve cells in their brains
Bees can solve seemingly clever counting tasks with very small numbers of nerve cells in their brains, according to researchers at Queen Mary University of London.

Read More: Nerve Cells News and Nerve Cells Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.