The ability to read is a uniquely human trait, one which has allowed us to pass on ideas, culture, and knowledge without being present, even after our death. Because of this ability, we are able to teach and inform ourselves which is something no other species has been able to do.
But what happens in the brain during the reading acquisition? How does this ability, which hasn't always been ours, change the function and structure of our brains? And are the modifications which occur due to it always beneficial or do we lose something from it too?
When deciding where to begin to look into what brain areas are affected by and implicated in reading acquisition, it's not a bad idea to begin by thinking about what skills are inherently involved in reading e.g. visual processing and language processing. These are mechanisms that lend themselves well to neuroimaging studies such as fMRI and in fact, such studies have been done.
This being said, most such studies have relied on subjects who are college students and are therefore both literate and well educated, meaning that most of the existing knowledge about the brain structures related to reading have been biased because of the sample they rely upon. However, there have been efforts to remedy this.
In their 2010 study, Dehaene et al. used fMRI to scan a total of 63 Portuguese and Brazilian participants. The sample included 32 un-schooled adults, of which there were 10 illiterates and 22 of what they termed "x-illiterates" (which had acquired reading in adulthood), and 31 schooled and literate adults, as well as a group of 11 literate adults matched to the illiterate ones in socio-economic status.
Their results pointed to three simple effects: the acquisition of literacy predicts an activation in the right Occipital Cortex at the same levels as checkerboards for written materials, it also means that reading induces a powerful activation in the left Ventral Visual Cortex at the site of an area called the Visual Word Form Area and activates the left Perisylvian Temporal and Frontal Language Areas.
Thus, literacy results in the emergence of a cortical site increasingly more responsive to writing than to other visual categories. (Dehaene et al., 2010)
The VWFA is generally agreed to be involved in the identification of orthographic stimuli and our ability to quickly associate this kind of stimuli with phonological and lexical information, there are, however, more than one view on how this happens.
One of these views is that the VWFA contains a highly specialized neural network for orthographic coding, some studies have even suggested that it may "sharply tune to known words" (Dehaene et al., 2015)
Another view suggests that this kind of tuning only happens because of top-down prediction effects in a generic circuit that bidirectionally links visual areas with language areas. (Dehaene et al., 2015)
According to Dehaene and colleagues' 2015 review of studies on illiterate subjects, "learning to read means developing an efficient interface between vision and spoken language", so it is not strange to find that the Ventral Occipito Temporal Cortex has been implicated, specifically at the VWFA but also at early visual cortices (V1 and V2), what is interesting though, is that the VWFA is located next to the left Fusiform Face Area (FFA) which is involved in facial recognition and in the processing of facial expressions.
It has been found that before reading acquisition the VWFA shows higher activity when presented with visual stimuli (e.g. tools, faces.) but during reading acquisition the boundaries between the VWFA and the FFA seem to shift, causing a face response displacement effect, where the VWFA is less activated by faces and activation moves to the right fusiform gyrus at the location of the FFA.
Ex illiterate adults show less reduction in face evoked responses than literate adults, which might point to face responses becoming fully established at adulthood to the point they will no longer be shifted by reading acquisition, this could perhaps be a hindrance to the speed and fluency that adults can reach when they acquire literacy. This effect is also absent in dyslexics but it's not known if it's due to dyslexia or another factor.
Another brain region affected by reading acquisition is the planum temporale, which contains neuronal representations of vowels and consonants of spoken language. The activation in this area has been shown to be doubled in literate subjects during auditory lexical decision tasks (such as deciding if a spoken item is a word) compared to illiterate subjects. In expert readers, the activation in the PT is enhanced when a vowel or letter presented is congruent with the spoken stimuli.
Anatomically speaking, the connections between the posterior corpus callosum and left arcuate are changed in a detectable manner (Dehaene et al., 2015) On a functional level this leads to more fluid and fast interaction between our internal representation of written symbols and spoken words.
In summary the acquisition of reading seems to affect the brain in such a way that it creates an "automating and efficient interface between vision and language" (Dehaene et al., 215) The sites affected are the left Ventral Occipitotemporal Cortex, where the VWFA is located as well as the bilateral occipital visual cortices and the left Superior Temporal regions such as the PT, the areas that see improvement are an extended network of surrounding occipitoparietal areas.
The way our actions shape the structures and functions of our brain is obviously a fascinating topic, this goes doubly with skills that we as a species have acquired uniquely, the structures and functions mentioned in this review are far from being all that there is to the way reading acquisition affects the brain and there are still further questions to be asked and areas of the brain to look into, one of these might for instance be the Anterior Temporal Circuits in relation to lexical meaning and syntax.
Whatever future studies bring to light, what we already know has made it clear that reading is an important way in which we as a species affect our own cognition and perception through learning and this alone should be a good enough reason for studying the effect of this acquired skill.