Cortical asymmetries at different spatial hierarchies relate to phonological processing ability

Abstract

The ability to map speech sounds to corresponding letters is critical for establishing proficient reading. People vary in this phonological processing ability, which has been hypothesized to result from variation in hemispheric asymmetries within brain regions that support language. A cerebral lateralization hypothesis predicts that more asymmetric brain structures facilitate the development of foundational reading skills like phonological processing. That is, structural asymmetries are predicted to linearly increase with ability. In contrast, a canalization hypothesis predicts that asymmetries constrain behavioral performance within a normal range. That is, structural asymmetries are predicted to quadratically relate to phonological processing, with average phonological processing occurring in people with the most asymmetric structures. These predictions were examined in relatively large samples of children (N = 424) and adults (N = 300), using a topological asymmetry analysis of T1-weighted brain images and a decoding measure of phonological processing. There was limited evidence of structural asymmetry and phonological decoding associations in classic language-related brain regions. However, and in modest support of the cerebral lateralization hypothesis, small to medium effect sizes were observed where phonological decoding accuracy increased with the magnitude of the largest structural asymmetry across left hemisphere cortical regions, but not right hemisphere cortical regions, for both the adult and pediatric samples. In support of the canalization hypothesis, small to medium effect sizes were observed where phonological decoding in the normal range was associated with increased asymmetries in specific cortical regions for both the adult and pediatric samples, which included performance monitoring and motor planning brain regions that contribute to oral and written language functions. Thus, the relevance of each hypothesis to phonological decoding may depend on the scale of brain organization.

A volumetric asymmetry study of gray matter in individuals with and without dyslexia

“…neurochemical makeup (Zilles & Amunts, 2018). However, there is still reason to explore the structural contribution of BA47 to reading ability as this region is involved in multiple reading processing (e.g., accessing semantics [Dickens et al, 2019], covert articulation [Hope et al, 2014], semantics articulation [Eckert et al, 2022], just to name a few). For example, Sabb et al (2007) explored the role of BA47 in working memory and found increased activity in the pars orbitalis for primed compared to unprimed items.…”

“…This region appears to be most distinct from BA45 and BA44, whereby BA47 has quite a different structural and neurochemical makeup (Zilles & Amunts, 2018). However, there is still reason to explore the structural contribution of BA47 to reading ability as this region is involved in multiple reading processing (e.g., accessing semantics [Dickens et al., 2019], covert articulation [Hope et al., 2014], semantics articulation [Eckert et al., 2022], just to name a few). For example, Sabb et al.…”

Sensory temporal sampling in time: an integrated model of the TSF and neural noise hypothesis as an etiological pathway for dyslexia

“…In the dyslexia literature, abnormalities in brain asymmetry in both cortical gray matter and white matter tracts from the language network have been documented, in both case studies/reviews (Galaburda et al, 1985 ; Geschwind and Galaburda, 1985 ; Leonard and Eckert, 2008 ); and cross-sectional research on dyslexia (see Duara et al, 1991 ; Niogi and McCandliss, 2006 ; Altarelli et al, 2014 ; Zhao et al, 2016 ; and Banfi et al, 2019 ). A recent large-scale cross-sectional study on both adults and children reported more modest effect sizes for asymmetry differences in cortical regions that are associated with phonological processing (Eckert et al, 2022 ). Correspondingly, one might expect there to be clear differences in cerebral asymmetry of cortical oscillations between typical and poor readers.…”

Dyslexia: Causes and Concomitant Impairments

“…The question of whether an impairment is a cause of DD or whether it is merely an accompanying deficit with no causal significance is also fundamental to the assessment of neural dysfunctions that may occur together with impaired abilities such as dyslexia [ 161 , 162 ]. Theories regarding the neural basis of DD mainly rely on functional magnetic resonance imaging (fMRI) studies [ 125 , 126 , 127 , 128 , 129 , 163 , 164 , 165 , 166 , 167 , 168 , 169 , 170 , 171 , 172 , 173 , 174 , 175 , 176 , 177 , 178 , 179 , 180 , 181 , 182 , 183 , 184 , 185 , 186 , 187 , 188 , 189 , 190 ]. An increase in the blood-oxygen-level-dependent (BOLD) signal in an area of the brain shows that this area is receiving sensory afferents or input from other brain areas [ 191 , 192 ].…”