Segregation of Lexical and Sub-Lexical Reading Processes in the Left Perisylvian Cortex

Abstract

A fundamental issue in cognitive neuroscience is the existence of two major, sub-lexical and lexical, reading processes and their possible segregation in the left posterior perisylvian cortex. Using cortical electrostimulation mapping, we identified the cortical areas involved on reading either orthographically irregular words (lexical, “direct” process) or pronounceable pseudowords (sublexical, “indirect” process) in 14 right-handed neurosurgical patients while video-recording behavioral effects. Intraoperative neuronavigation system and Montreal Neurological Institute (MNI) stereotactic coordinates were used to identify the localization of stimulation sites. Fifty-one reading interference areas were found that affected either words (14 areas), or pseudo-words (11 areas), or both (26 areas). Forty-one (80%) corresponded to the impairment of the phonological level of reading processes. Reading processes involved discrete, highly localized perisylvian cortical areas with individual variability. MNI coordinates throughout the group exhibited a clear segregation according to the tested reading route; specific pseudo-word reading interferences were concentrated in a restricted inferior and anterior subpart of the left supramarginal gyrus (barycentre x = −68.1; y = −25.9; z = 30.2; Brodmann’s area 40) while specific word reading areas were located almost exclusively alongside the left superior temporal gyrus. Although half of the reading interferences found were nonspecific, the finding of specific lexical or sublexical interferences is new evidence that lexical and sublexical processes of reading could be partially supported by distinct cortical sub-regions despite their anatomical proximity. These data are in line with many brain activation studies that showed that left superior temporal and inferior parietal regions had a crucial role respectively in word and pseudoword reading and were core regions for dyslexia.

Electrostimulation mapping of comprehension of auditory and visual words

“…Electrostimulation of some areas in this gyrus showed that phonological lexical representations could also be affected in isolation, without semantic interferences, as already suggested in previous studies focusing not on auditory tasks but on word reading(Simos, Breier, Fletcher, Foorman & Castillo, 2002;Roux, Durand, Jucla, Rehault, Reddy & Demonet 2012). In the naming process, this region would harbour the neural populations that support the phonological output component of naming, just upstream of the involvement of the articulatory functional areas in the Rolandic region needed to pronounce the target word.In conclusion, these findings are in line with the current conceptualizations of the neural correlates of speech comprehension.…”

The “handwriting brain”: A meta-analysis of neuroimaging studies of motor versus orthographic processes

“…It is associated with both phonological agraphia, a writing disturbance characterized by an inability to write pseudowords (Alexander et al, 1992b) and phonological dyslexia, i.e., the associated deficit in reading (Beauvois and Derouesne, 1979). Specific pseudoword reading disturbances have recently been observed with direct cortical stimulation of the SMG (Roux et al, 2012). Moreover, the phonological processes supported by the left perisylvian region are believed to be modality-independent and shared between reading and spelling abilities (Rapcsak et al, 2009).…”

Balanced bilinguals favor lexical processing in their opaque language and conversion system in their shallow language

“…Regular and unfamiliar word or non-word reading may preferentially rely on phonological pathways, where each grapheme is sequentially mapped to its corresponding phoneme. Neural correlates of phonological processing have most commonly been identified within superior temporal (Graves, Grabowski, Mehta, & Gupta, 2008;Jobard et al, 2003), supramarginal (Graves et al, 2008;Jobard et al, 2003;Roux et al, 2012), insular (Binder et al, 2005;Fiez, Balota, Raichle, & Petersen, 1999;Herbster, Mintun, Nebes, & Becker, 1997) and inferior frontal regions/pars opercularis; BA44; e.g. Jobard et al, 2003;Nixon, Lazarova, Hodinott-Hill, Gough, & Passingham, 2004;Binder et al, 2005).…”