© Max Planck Institute for Human Cognitive and Brain Sciences
Kvindelige analfabeter i det nordlige Indien lærte at læse og skrive igennem et forløb, der strakte sig over seks måneder, hvorefter de nåede et niveau svarende til første klasse.
Et nyt forskningsresultat viser, den menneskelige hjerne må sammensætte et netværk, der håndterer læsning, ved at omgruppere anvendelsen af dybtliggende områder i hjernen, så den kan udføre en visuelt-sprogligt funktion. Forskningsholdet meddeler, at hjernen er i stand til at håndtere denne proces med overraskende lethed.

I et udviklingsperspektiv er læsning hos mennesker af ny dato - for slet ikke at nævne den udbredte og almindeligt anvendte kombination af læsning og skrivning. På grund af dette har vi ikke udviklet en specifik region i hjernen, der kan håndtere denne proces.

Så hvad gør man, så hvis man er en hjerne i et menneske, og man ikke har lært at skabe mening ud fra disse streger og mærker? Man improviserer selvfølgelig! Idet man fortsætter med at fungere inden for hjerneskallens grænser, handler denne improvisering om at omlægge brugen af hjernen, således at nogle områder i den del af hjernebarken, der bearbejder synsimpulser, og som almindeligvis håndterer kompleks formgenkendelse, optrænes til at udføre den opgave at genkende disse streger og mærker. Samtidig påtager nogle af de ældste eller tidlige dele af hjernen sig den rolle at skabe forbindelse mellem det sproglige system og det visuelle system.

Gammel hjerne, nye tricks

Den kendsgerning, at det at lærer at læse fører til fysiske ændringer i hjernen, så som skabelsen af nye nervebaner, er ikke just nyt. Men indtil nu har vi troet, at de ændringer, som tekstlæsning bringer er afgrænset til hjernebarken, de ydre lag af hjernen, som håndterer de højere mentale funktioner, og som hurtigt kan tilpasse sig, så den kan mestre nye færdigheder og overvinde udfordringer.


However, a team led by Falk Huettig from the Max Planck Institute for Psycholinguistics found that the brain does a lot more heavy lifting to master literacy. The Max Plank team worked together with scientists from the Centre of Bio-Medical Research (CBMR) in Lucknow, India, and the University of Hyderabad to uncover how the brains of completely illiterate people change when they learn to read and write.

For the study, the researchers worked with people in India. Illiteracy is pretty high here, mostly due to poverty, going at a rate of roughly 38% of the population but strongly skewed towards women. The team worked with an all-women group of participants, almost all of them in their thirties. They were recruited from the same social class in two villages in Northern India to take social factors out of the final results. Participants were further matched for handedness, income, number of literate family members and took two initial measures of literacy (letter identification and word-reading ability.) Lastly, they each had their brains scanned in the city of Lucknow.

After the team had enough data to form a baseline, the women were given a 6-months long period of reading training in their native tongue of Hindi, one of the official languages of India. It is based on Devanagari, that distinctive Indian and Nepalese flowing script, a style of writing known as an alphasyllabary. In alphasyllabary, you don't write with single letters but with whole syllables or words at a time, in consonant-vowel pairings (written in that order).

At the start of their training, the vast majority of the participants couldn't read a single word in Hindi. But after only six months, they reached roughly the same reading proficiency as a first-grader, quite an impressive result.

"While it is quite difficult for us to learn a new language, it appears to be much easier for us to learn to read," says Huettig. "The adult brain proves to be astonishingly flexible."

Deep re-purposing

The team reports that the functional reorganization extends all the way to the deep, early-brain structures of the thalamus and the brainstem. These are very old brain areas, evolutionary speaking, and are universally found in mammalian brains as well as other species.

"We observed that the so-called colliculi superiores, a part of the brainstem, and the pulvinar, located in the thalamus, adapt the timing of their activity patterns to those of the visual cortex," says Michael Skeide, scientific researcher at the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) in Leipzig and first author of the study.

These areas take on a sort of interface role, helping the visual cortex filter relevant visual stimuli — in this case, writing — from the wealth of information our eyes supply even before we become consciously aware of it. Skeide notes that "the more the signal timings between the two brain regions are aligned, the better the reading capabilities." This would, of course, happen with practice, explaining why experienced readers can easily take in a text which would leave an aspiring reader scrambling for help.

The findings could help uncover the causes of reading disorders such as dyslexia. The condition has previously been linked to abnormal activity in the thalamus, an avenue of research Skeide says the team has "to scrutinize" considering they showed "that only a few months of reading training can modify the thalamus fundamentally."

Finally, the findings should come as a boon to anyone currently struggling with illiteracy, especially in the West where it's such a taboo subject and the object of social stigma.

The full article "Learning to read alters cortico-subcortical cross-talk in the visual system of illiterates" has been published in the journal Science Advances.