Eisner, F., Kumar, U., Mishra, R. K., Nand Tripathi, V., Guleria, A., Singh, P., & Huettig, F.
(2015). The effect of literacy acquisition on cortical and subcortical networks: A longitudinal approach. Talk presented at the 7th Annual Meeting of the Society for the Neurobiology of Language. Chicago, US. 2015-10-15 - 2015-10-17.
How do human cultural inventions such as reading result
in neural re-organization? Previous cross-sectional studies
have reported extensive effects of literacy on the neural
systems for vision and language (Dehaene et al [2010,
Science], Castro-Caldas et al [1998, Brain], Petersson et
al [1998, NeuroImage], Carreiras et al [2009, Nature]).
In this first longitudinal study with completely illiterate
participants, we measured brain responses to speech, text,
and other categories of visual stimuli with fMRI before and
after a group of illiterate participants in India completed
a literacy training program in which they learned to read
and write Devanagari script. A literate and an illiterate
no-training control group were matched to the training
group in terms of socioeconomic background and were
recruited from the same societal community in two villages
of a rural area near Lucknow, India. This design permitted
investigating effects of literacy cross-sectionally across
groups before training (N=86) as well as longitudinally
(training group N=25). The two analysis approaches
yielded converging results: Literacy was associated with
enhanced, mainly left-lateralized responses to written
text along the ventral stream (including lingual gyrus,
fusiform gyrus, and parahippocampal gyrus), dorsal
stream (intraparietal sulcus), and (pre-) motor systems
(pre-central sulcus, supplementary motor area), thalamus
(pulvinar), and cerebellum. Significantly reduced responses
were observed bilaterally in the superior parietal lobe
(precuneus) and in the right angular gyrus. These positive
effects corroborate and extend previous findings from
cross-sectional studies. However, effects of literacy were
specific to written text and (to a lesser extent) to false fonts.
Contrary to previous research, we found no direct evidence
of literacy affecting the processing of other types of visual
stimuli such as faces, tools, houses, and checkerboards.
Furthermore, unlike in some previous studies, we did not
find any evidence for effects of literacy on responses in
the auditory cortex in our Hindi-speaking participants.
We conclude that learning to read has a specific and
extensive effect on the processing of written text along
the visual pathways, including low-level thalamic nuclei,
high-level systems in the intraparietal sulcus and the
fusiform gyrus, and motor areas. The absence of an effect
of literacy on responses in the auditory cortex in particular
raises questions about the extent to which phonological
representations in the auditory cortex are altered by
literacy acquisition or recruited online during reading.