Authors: Seghier ML, Neufeld NH, Zeidman P, Leff AP, Mechelli A, Nagendran A, Riddoch JM, Humphreys GW, Price CJ..
Publication: Neuropsychologia (Elsevier). 50(14), 3621-3635 2012 | DOI: 10.1016/j.neuropsychologia.2012.09.030
► Word reading can succeed after damage to the left occipito-temporal cortex.
► This is enabled by an alternative pathway via the left superior temporal sulcus.
► Connectivity analysis demonstrated the existence of this pathway in normal readers.
► We hypothesise that this pathway integrates semantics with phonology.
► Our work stresses the importance of mapping alternative degenerate reading pathways.
The left ventral occipito-temporal cortex (LvOT) is thought to be essential for the rapid parallel letter processing that is required for skilled reading. Here we investigate whether rapid written word identification in skilled readers can be supported by neural pathways that do not involve LvOT. Hypotheses were derived from a stroke patient who acquired dyslexia following extensive LvOT damage. The patient followed a reading trajectory typical of that associated with pure alexia, re-gaining the ability to read aloud many words with declining performance as the length of words increased. Using functional MRI and dynamic causal modelling (DCM), we found that, when short (three to five letter) familiar words were read successfully, visual inputs to the patient’s occipital cortex were connected to left motor and premotor regions via activity in a central part of the left superior temporal sulcus (STS). The patient analysis therefore implied a left hemisphere “reading-without-LvOT” pathway that involved STS. We then investigated whether the same reading-without-LvOT pathway could be identified in 29 skilled readers and whether there was inter-subject variability in the degree to which skilled reading engaged LvOT. We found that functional connectivity in the reading-without-LvOT pathway was strongest in individuals who had the weakest functional connectivity in the LvOT pathway. This observation validates the findings of our patient’s case study. Our findings highlight the contribution of a left hemisphere reading pathway that is activated during the rapid identification of short familiar written words, particularly when LvOT is not involved. Preservation and use of this pathway may explain how patients are still able to read short words accurately when LvOT has been damaged.
Seghier, M. L., Neufeld, N. H., Zeidman, P., Leff, A. P., Mechelli, A., Nagendran, A., … & Price, C. J. (2012). Reading without the left ventral occipito-temporal cortex. Neuropsychologia, 50(14), 3621-3635.
The STS pathway was also observed in healthy skilled readers
and was found to be dissociable from the LvOT pathway. This
finding is in line with previous studies that demonstrate how
skilled reading can be sustained by multiple neural pathways.
Our work has theoretical implications for understanding the
neural systems that support reading. Current reading models
typically assume that LvOT plays an essential role in reading by
linking visual inputs to the language system (see recent reviews
in (Dehaene & Cohen, 2011; Price & Devlin, 2011; Wandell, 2011).
However, our data suggest that, although loss of LvOT impairs
reading, it is still possible to have relatively rapid access to the left
hemisphere language system for short familiar words. This is in
line with recent evidence (Richardson et al., 2011) that activation
during silent reading in healthy skilled readers is better explained
by models that connect the occipital cortex to the language
system via two pathways (one with and one without LvOT) rather
than one pathway (either with or without LvOT). However, the
current study goes beyond this previous observation by demonstrating that (1) the reading-without-LvOT pathway is sufficient
to support some degree of rapid word identification when the
reading-with-LvOT pathway is damaged; (2) in healthy skilled
readers, modulation of functional connectivity during naming and
reading in the reading-without-LvOT pathway is stronger when
there is weaker modulation of functional connectivity in the reading-with-LvOT pathway; and (3) the reading without LvOT
pathway involves an STS area that is associated with semantic to
Our findings also have implications for cognitive models of reading. Previous neuropsychological and computational reading models have dissociated different semantic and non-semantic reading routes …. By dissociating the LvOT reading pathway
from the STS reading pathway, our results further support the
existence of more than one reading route. Moreover, we have
suggested above that (i) the superior parietal cortices are involved
in an additional pathway that is involved in attention demanding
contexts; and (ii) the inferior parietal cortices are involved in spelling to sound translation. The independence of each of these reading pathways on behaviour warrants further investigation.