When damage to the left hemisphere of the brain in the process of fetal development of language functions take on appropriate sites in the right hemisphere, discovered by European scientists. To do this, they conducted an fMRI experiment with the participation of children even before birth suffered an ischemic stroke that resulted in damage to the left hemisphere. It turned out that after damage to the frontal and temporal lobes of the left hemisphere of the reorganization undertaken by them speech functions in the same areas of the right hemisphere, and from the strength of established relationships depended on how developed was language ability, write the scientists in the journal eNeuro.
Stroke is accompanied by poor circulation in the brain, which can lead to extensive damage to its structure. Very often in these cases are violated and the functions that the damaged areas of the brain answer: so, for example, stroke often causes paralysis of the limbs or body as a whole.
The stroke of the speech centers of the brain occurs aphasia is an acquired speech disorder. Despite the fact that the type of aphasia and severity of acquired disorders depends on which area of the brain affected, the most serious speech, the consequences of the damage to the frontal and temporal lobes of the left hemisphere: these are areas (particularly Broca’s area and Wernicke area) for the production and understanding of speech are basic.
In the process of intensive care after suffering a stroke, lost speech function can partially (rarely completely) recover. It is believed that to take over the job of damaged areas can those same departments, but in the right hemisphere. The mechanism of this reorganization are still not fully understood, particularly little is known about its foundations in the process of early brain development.
To study the reorganization of speech departments of a brain after a stroke, moved in the process of fetal development, decided by scientists under the leadership of clément françois (François Clément) from the University of Barcelona. Their study involved six four-year-olds with ischemic (due to blockage or narrowing of arteries) stroke in the left hemisphere and nine children of the same age without the trauma of a brain.
All participants underwent several tests for assessment of cognitive functions (memory, attention, learning abilities, etc), vocabulary, phonological production (in particular, pronunciation of individual sounds and words) and the complexity and completeness of speech production (for this whole analyzed speech samples of the participants: for example, the number of different words in told their stories, as well as the presence of pauses and hesitation). After that, the researchers conducted two fMRI experiment: in the resting state to further investigate the integrity of tissue and circuits of the brain, and the experiment in which we studied the brain activity when listening to stories.
In General, children who have had a stroke, did not differ from their peers in the control group on the indicators for assessing cognitive abilities: their performance was at an average level, characteristic for normal development of four year-olds. However, the indicators of abilities to phonological processing, memorizing speeches and other information were on a level slightly below normal. The significant breaches in the understanding and production of speech was observed only in one child from the group of stroke survivors: his speech differed significantly (p = 0.002) reduced complexity.
Evaluation after stroke, brain injury indicated a major loss of white, but not gray matter: it was observed in four of six children that has allowed scientists to make the assumption that in the course of a stroke suffered precisely the tracts of white matter. In the course of an fMRI experiment with listening to the stories from children of stroke survivors, there is increased activity in the middle temporal and inferior frontal gyri in the right hemisphere in contrast with the same areas that are active from the intact brain in the left hemisphere. With regard to the anatomical features of the right hemisphere of the brain of these children, scientists have observed good preservation of white matter tracts that connect language centers in the frontal and temporal lobes — again, exactly the same as in the left hemisphere of the brain without suffering a stroke. Interestingly, the strength of these tracts was correlated positively (p < 0.0001) with the results of speech tests: in other words, how well it was reorganized to the right hemisphere after damage to the left depended on how much was intact speech function of the child.
If it is impossible the normal development of speech through the left hemisphere, the authors conclude, there is reorganization in the right: damage to the speech centers of the left hemisphere in the process of fetal development leads to the fact that their inherent functions take on the same region in the intact hemisphere. The success of the development of speech functions, in particular, depends on how such a migration was successful: that is, how well lined up the necessary connections in new areas. It depends on interhemispheric plasticity — that is, how well the sections of the two hemispheres are connected to each other functionally; however, the successful development of speech skills with previous stroke is still likely to depend on behavioural development of the child: all members of the active experimental group were the lessons from speech therapists and other professionals on speech development.
It is also worth noting that new information obtained by scientists say about the plasticity of the development of speech functions in the brain. In particular the fact that damage to the left hemisphere of its functions of production and understanding of speech takes on the right, suggests that the lateralization of these functions is quite flexible and not formed to the end during fetal development.
It should again be clarified that the recovery of speech functions after a stroke and needed intensive therapy. It requires constant monitoring of the speech of the patient: most of it is done through the analysis of audio recordings, but there are other methods. For example, last year, American engineers introduced a special skin sensor that increases the accuracy of speech analysis, recording of the movement of the vocal folds.