We will speak about neuronal plasticity, the flexibility of the brain, that amazing phenomenon in which some neurons are born and others die; the dendrites change their branching pattern or they are pruned, the synapses are created, divided, eliminated or become more or less powerful. This process is the basis of memory and learning and, in turn, memory and learning modify the brain.
Neural plasticity exists in all ages and that allows us to learn in adult life.
Neural Plasticity. How far does this effect lasts?
That’s what Michael Skeide and his colleagues at the Max Planck Institute for Brain and Cognitive Sciences in Leipzig, Germany, have come up with. This group works on the normal and altered development of language and literacy, using mostly a combination of high resolution magnetic resonance techniques in combination with behavioral data and gene sequencing.
Learning to read is an intense cultural experience that requires systematic training and intense practice for months or years. The changes in the blood supply to the brain induced by perceiving printed letters change within a few weeks of beginning to work on the letter-sound relationship. Shortly thereafter, a functional selectivity to print appears in the visual system – in the bilateral occipital cortex – and in a region that processes multimodal symbols that are located in the left temporal-occipital fusiform cortex. In other words, the learning of the reading sets in motion cognitive adaptations that are manifested in an increase of the oxygen consumption in brain areas during the processing of the printed letter. Until now there were doubts about whether the acquisition of reading generated an intrinsic reorganization of the neural circuits. Now we know that it is like that.
How do you know to what extent culture is capable of modifying the brain and how it does it?
They studied a group of illiterate adults and taught them how to read and write. It is interesting because reading and writing, those two sublime activities of the human brain, are very recent evolutionarily and, therefore, have not had time to generate a genetic substrate. Neither is there a brain area dedicated specifically to reading. In other words, we do not have genes to read and write and we use neural circuits that already existed, for example to distinguish details in a broader vision. When we learn to read our brain, it realizes a kind of realignment: areas that evolved for the recognition of complex objects, such as faces, are in charge of translating letters into language and some regions of our visual system become interfaces between the visual system and the language system.
Researchers recruited thirty Hindi-speaking adults from two villages near the Indian city of Lucknow, aged 31 years. Twenty-one of them were taught to read and write with the letter Devanagari, which is used for Hindi and other languages of the Indian subcontinent. The other nine, who were not taught to read and write in that period, served as controls. They all had a brain scan before and after the six-month period.
The main result is that at the end of the study the German team found significant changes in the brains of people who had learned to read and write. They showed an increase in brain activity in the cortex, the outermost portion of the cerebral hemispheres, which is responsible, among other learning functions. That is something known because literacy generates a cortical reorganization. But what was more striking is that learning to read also changes brain regions that do not have to do, in principle, with reading, writing or learning. The researchers saw that the neuronal plasticity induced by literacy also increased functional connectivity between the occipital lobe and subcortical areas in the brainstem (right upper colliculus) and the thalamus (bilateral pulvinary nuclei). These areas adapted their discharge patterns to those of the visual cortex. Moreover, how much more synchronized were the times of that neuronal activity in both regions, the better was the ability to read: therefore it seems that these systems adjust their communication better and better as a person is reading better. This may explain why an experienced reader navigates a text with much greater efficiency.
These results suggest that a reconceptualization of the neural base of the reading has to be done, expanding the experimental approach from one centered exclusively in the cortex to one that also includes these subcortical areas associated with oculomotor control and selective visuospatial attention.
The most plausible explanation for this greater degree of activity is that these regions coordinate information about our senses and our eye movements, among other tasks. Both areas showed a greater development of connections with the cortical region that processes vision after learning to read. Another interesting result is that the people who showed the most striking changes were those who had made the most progress in their ability to read during the training period.
It is complicated in these studies to establish direct relationships. For example, the brainstem and the thalamus are also responsible for controlling attention, a skill that is needed to read and also that is exercised, and probably reinforced, by reading. Therefore, reading sets in motion important cognitive processes and also involves the development of important sensorimotor skills, including the need for fine control of eye movements to sweep line after line of text and to move the eyes in the most informative areas .
It is very likely that these changes will occur in the same way in children who are learning to read and write, and the most logical thing is that in those developing brains the changes are more intense, but no similar studies have been done in that timeframe. age.
On the other hand it is possible that this line of research can provide useful information about dyslexia. Until now it was known that affected people have differences in the structure and function of the thalamus compared to neurotypical people. Since the thalamic connections present changes after an intensive literacy course it is possible that the absence of a reading experience, or its scarcity or anomaly as it can happen in the dyslexia, generate those changes. That is, the real cause of dyslexia would not be anomalous thalamic connections, but dyslexia could be the cause of thalamic alterations.