Atypical Balance between Occipital and Fronto-Parietal Activation for Visual Shape Extraction in Dyslexia

Abstract

Reading requires the extraction of letter shapes from a complex background of text, and an impairment in visual shape extraction would cause difficulty in reading. To investigate the neural mechanisms of visual shape extraction in dyslexia, we used functional magnetic resonance imaging (fMRI) to examine brain activation while adults with or without dyslexia responded to the change of an arrow’s direction in a complex, relative to a simple, visual background. In comparison to adults with typical reading ability, adults with dyslexia exhibited opposite patterns of atypical activation: decreased activation in occipital visual areas associated with visual perception, and increased activation in frontal and parietal regions associated with visual attention. These findings indicate that dyslexia involves atypical brain organization for fundamental processes of visual shape extraction even when reading is not involved. Overengagement in higher-order association cortices, required to compensate for underengagment in lower-order visual cortices, may result in competition for top-down attentional resources helpful for fluent reading.

Brain Mechanisms Underlying Visuo-Orthographic Deficits in Children With Developmental Dyslexia

“…In the perceptual task, the DD group showed increased functional connectivity between these two regions compared to AC, but not RC. The LMOG is commonly understood to be responsible for visuo-orthographic processing during written word tasks (Zhang et al, 2013; Cao et al, 2017), while the left IFG plays an important role in phoneme segmentation and manipulation (Booth et al, 2007; Cone et al, 2008). It appears that our finding suggests a reduced interaction between orthography and phonology in DD which is consistent with previous studies (Booth et al, 1999, 2000; Plaut and Booth, 2000; Desroches et al, 2010; Cao et al, 2017).…”

“…Neurologically speaking, readers with dyslexia exhibit abnormal brain activation during visual and orthographic processing tasks. For example, it has been reported that, compared to controls, people with dyslexia exhibit decreased activation in the middle occipital gyrus (MOG) during visual-perception tasks such as number identification (Boros et al, 2016), symbol detection (Boros et al, 2016), and arrow shape judgment (Zhang et al, 2013). Interestingly, decreased activation in the MOG has also been reported for orthographic tasks that involve pseudoword reading (Shaywitz et al, 2002; Van der Mark et al, 2009; Dehaene et al, 2010; Boros et al, 2016), lexical decision making (Siok et al, 2004), font judgment (Siok et al, 2008), letter matching (Temple et al, 2001), and letter identification (Boros et al, 2016).…”

Neurogenetics of developmental dyslexia: from genes to behavior through brain neuroimaging and cognitive and sensorial mechanisms

“…Visual spatial tasks elicited altered activation in the right temporal (temporal pole, fusiform gyrus, temporal gyrus, motor/premotor cortex) and frontal (precentral gyrus, frontal gyrus) areas, and in bilateral parietal (intraparietal sulcus, inferior and superior parietal lobes, precuneus), occipital (cuneus, BAs 17–19), subcortical structures (putamen, basal ganglia), anterior cingulate and cerebellum. 157 , 166 , 177 , 178 …”

Dysfunction of Rapid Neural Adaptation in Dyslexia

“…Moreover, neural adaptation in sensory cortices to the consistent features of perceptual noise has been shown to be an important mechanism for improving perception in adverse conditions (Atiani et al, 2009). A large behavioral literature now shows that perceptual noise is significantly more detrimental to individuals with dyslexia than controls across auditory, visual, verbal, and non-verbal tasks (Chait et al, 2007; Sperling et al, 2005, 2006; Ziegler et al, 2009), with neural evidence also showing noise-exclusion deficits in dyslexia (White-Schwoch et al, 2015; Zhang et al, 2013). Based on these behavioral effects in dyslexia, and corresponding neurophysiological effects in animal models and humans, we hypothesized that rapid neural adaptation may be dysfunctional in individuals with dyslexia.…”