a bonobo humanity?

a one-sided view (the left) of the parts of the brain involved in language and reading processing

Canto: So we’re still looking at automaticity, and it’s long been observed that dyslexic kids have trouble retrieving names of both letters and objects from age three, and then with time the problem with letters becomes more prominent. This means that there just might be a way of diagnosing dyslexia from early problems with object naming, which of course starts first.

Jacinta: And Wolf is saying that it may not be just slowness but the use of different neural pathways, which fMRI could reveal.

Canto: Well, Wolf suggests possibly the use of right-hemisphere circuitry. Anyway, here’s what she says re the future of this research:

It is my hope that future researchers will be able to image object naming before children ever learn to read, so that we can study whether the use of a particular set of structures in a circuit might be a cause or a consequence of not being able to adapt to the new task of literacy (Wolf, p181). 

So that takes us to the next section: “An impediment in the circuit connections among the structures”.

Jacinta: Connections between. And if we’re talking about the two hemispheres, the corpus callosum could’ve provided a barrier, as it does with stroke victims…

Canto: Yes, connections within the overall reading circuit, which involves different parts of the brain, can be more important for reaching automaticity than the brain regions themselves, and a lot of neuroscientists are exploring this connectivity. Apparently, according to Wolf, three forms of disconnections are being focussed on by researchers. One is an apparent disconnection ‘between frontal and posterior language regions, based on underactivity in an expansive connecting area called the insula. This important region mediates between relatively distant brain regions and is critical for automatic processing’ (Wolf, p182). Another area of disconnection involves the occipital-temporal region, also known as Brodmann area 37, which is activated by reading in all languages. Normally, strong, automatic connections are created between this posterior region and frontal regions in the left hemisphere, but dyslexic people make connections between the left occipital-temporal area and the right-hemisphere frontal areas. It also seems to be the case that in dyslexics the left angular gyrus, accessed by good beginning readers, doesn’t effectively connect with other left-hemisphere language regions during reading and the processing of phonemes.

Jacinta: And it’s not just fMRI that’s used for neuro-imaging. There’s something called magnetoencephalography (a great word for dyslexics) – or MEG – that gives an ‘approximate’ account of the regions activated during reading, and using this tool a US research group found that children with dyslexia were using a completely different reading circuitry, which helps explain the underactivity in other regions observed by other researchers.

Canto: And leads to provocative suggestions of a differently arranged brain in some people. Which takes us to the last of the four principles: ‘a different circuit for reading’. In this section, Wolf begins by recounting the  ideas of the neurologists Samuel T Orton and Anna Gillingham in the 1920s and 1930s. Orton rejected the term ‘dyslexia’, preferring ‘strephosymbolia’. Somehow it didn’t catch on, but essentially it means ‘twisted symbols’. He hypothesised that in the non-dyslexic, the left-hemisphere processes identify the correct orientation of letters and letter sequences, but in the dyslexic this identification was somehow hampered by a problem with left-right brain communication. And decades later, in the 70s this hypothesis appeared to be validated, in that tests on children in which they were given ‘dichotic tasks’ – to identify varied auditory signals presented to different ears – revealed that impaired readers didn’t use left-hemisphere auditory processes in the same way as average readers. Other research showed that dyslexic readers showed ‘right-hemisphere superiority’, by which I think is meant that they favoured the right hemisphere for tasks usually favoured by the left.

Jacinta: Yes, weakness in the left hemisphere for handling linguistic tasks. But a lot of this was dismissed, or questioned, for being overly simplistic. You know, the old left-brain right-brain dichotomy that was in vogue in popular psychology some 30 years ago. Here’s what Wolf, very much a leading expert in this field, has to say on the latest findings (well, circa 2010):

In ongoing studies of the neural of typical reading, the research group at Georgetown University [a private research university in Washington DC] found that over time there is ‘progressive disengagement’ of the right hemisphere’s larger visual recognition system in reading words, and an increasing engagement of left hemisphere’s frontal, temporal, and occipital-temporal regions. This supports Orton’s belief that during development the left hemisphere takes over the processing of words (Wolf, p185).

Canto: Yes, that’s ‘typical reading’.  Children with dyslexia ‘used more frontal regions, and also showed much less activity in left posterior regions, particularly in the developmentally important left-hemisphere angular gyrus’. Basically, they used ‘auxiliary’ right-hemisphere regions to compensate for these apparently insufficiently functional left regions. It seems that they are using ‘memory’ strategies (from right-hemisphere structures) rather than analytic ones, and this causes highly predictable delays in processing. 

Jacinta: A number of brain regions are named in this explanation/exploration of the problems/solutions for dyslexic learners, and these names mean very little to us, so let’s provide some – very basic – descriptions of their known functions, and their positions in the brain. 

Canto: Right (or left):

The angular gyrus – which, like all other regions, is worth looking up on google images as to placement – is in a sense divided in two by the corpus callosum. Described as ‘horseshoe-shaped’, it’s in the parietal lobe, or more specifically ‘the posterior region of the inferior parietal lobe’. The parietal lobes are paired regions at the top and back of the brain, the superior sitting atop the inferior. The angular gyrus is the essential region for reading and writing, so it comes first. 

The occipital-temporal zone presumably implies a combo of the occipital and temporal lobes. The occipital is the smallest of the four lobes (occipital, temporal, parietal, frontal), each of which is ‘sided’, left and right. The junction of these two lobes with the parietal (TPO junction) is heavily involved in language processing as well as many other high-order functions.

Jacinta: Okay, that’ll do. It’s those delays you mention, the inability to attain automaticity, which characterises the dyslexic, and it appears to be caused by the use of a different brain circuitry, circuitry of the right-hemisphere. Best to quote Wolf again:

The dyslexic brain consistently employs more right-hemisphere structures than left-hemisphere structures, beginning with visual association areas and the occipital-temporal zone, extending through the right angular gyrus, supramarginal gyrus, and temporal regions. There is bilateral use of pivotal frontal regions, but this frontal activation is delayed (Wolf, p186).

Canto: The supramarginal gyrus is located just in front of and connected to the angular gyrus (a gyrus is anatomically defined as ‘a ridge or fold between two clefts on the cerebral surface in the brain). These two gyri, as mentioned above, make up the inferior parietal lobe. 

Jacinta: Wolf describes cumulative research from many parts of the world which tends towards a distinctive pattern in dyslexia, but also urges skepticism – the human brain’s complexity is almost too much for a mere human brain to comprehend. No two brains are precisely alike, and there’s unlikely to be a one-size-fits all cause or treatment, but explorations of this deficit are of course leading to a more detailed understanding of the brain’s processes involving particular types of object recognition, in visual and auditory terms. 

Canto: It’s certainly a tantalising field, and we’ve barely touched on the surface, and we’ve certainly not covered any, or very much of the latest research. One of the obvious questions is why some brains resort to different pathways from the majority, and whether there are upsides to offset the downsides. Is there some clue in the achievements of people known or suspected to be have been dyslexic in the past? I feel rather jealous of those researchers who are trying to solve these riddles….

References

Maryanne Wolf, Proust and the squid: the story and science of the reading brain, 2010

https://www.kenhub.com/en/library/anatomy/angular-gyrus

https://academic.oup.com/brain/article/126/9/2093/367492

https://en.wikipedia.org/wiki/Supramarginal_gyrus#:~:text=The%20supramarginal%20gyrus%20is%20part,of%20the%20mirror%20neuron%20system.