The left dominance only becomes apparent later: In contrast to adults, children are more likely to use both hemispheres of the brain for speech recording, according to a study. The results thus suggest a special importance of the right hemisphere during language development. They could also explain why children recover comparatively well from left-sided brain injuries, the scientists say.
Where in our brain are certain cognitive tasks performed? As far as the processing of spoken auditory impressions is concerned, studies have so far shown that areas in the left hemisphere are responsible for this in most people. As a rule, however, the right hemisphere shows comparatively little activity when grasping speech. This is also reflected in the fact that people who have had a left-sided stroke are often affected by irreversible loss of speech.
Questioning look at the brain hemispheres
So far, however, there has been a riddle: small children can develop or regain language skills, even if their left hemisphere is severely damaged – their right hemisphere can apparently partially compensate for the failures. One possible explanation for this flexibility would be that language processing early in life still relies on activity in both hemispheres of the brain. So far, however, there has been no clear evidence of this. “It was unclear whether there was strong left-wing dominance for language at birth or if it was gradual in development,” said Elissa Newport of Georgetown University Medical Center in Washington. She and her team have now investigated this question through detailed examinations using functional magnetic resonance imaging (fMRI).
39 healthy children between the ages of 4 and 13 and 14 adults between the ages of 18 and 29 took part in the study. While the brain activity of all study participants was recorded in detail by the fMRI in both hemispheres, they were given a task that required the understanding of spoken sentences. The researchers then compared the resulting patterns of brain activity in the test subjects, which they assigned to four age groups: 4 to 6, 7 to 9, 10 to 13 and 18 to 29 years.
The evaluations of the brain scans showed that, in principle, the left hemisphere of the brain also dominates language processing in small children. But in contrast to adults, brain regions in the right hemisphere also still show significant activity. These are areas that correspond to those on the left. In adults, however, according to the researchers, they are usually activated in other tasks – for example, when processing emotions that are expressed with the voice.
Right activity is emerging
In the smaller children, on the other hand, the corresponding areas in both hemispheres are busy understanding the meaning of sentences and recognizing the emotional impact, say the scientists. This processing pattern then shifts systematically with increasing age, according to the research results. “The comparatively high activation of the areas in the right hemisphere during sentence processing tasks and the slow decrease in this activation in the course of development is probably an expression of changes in the neural distribution of language functions,” says Newport.
In addition to the possible significance for brain development, the researchers now see the finding as a possible explanation for the fact that children recover from left-sided nerve injuries much more easily than adults. “Using both hemispheres apparently offers a means of compensation. If the left side is damaged by a stroke that occurred immediately after birth, the child can learn language using the right hemisphere. Our study shows how that could be possible, ”says Newport. “We now have a better basis on which to better understand brain injuries and recovery,” said the scientist.
You and your colleagues now want to stay on the ball: They plan to extend their examinations to even younger children. “We might see even greater functional right hemisphere involvement in speech processing in smaller people than our youngest study participants,” Newport says. In addition, the researchers now want to study speech activation in teenagers and young adults who suffered a severe stroke in the left hemisphere of the brain at birth.
Source: Georgetown University Medical Center, Article: PNAS, doi: 10.1073 / pnas.1905590117