Anatomical correlates of dyslexia: frontal and cerebellar findings

Abstract

In this study, we examined the neuroanatomy of dyslexic (14 males, four females) and control (19 males, 13 females) children in grades 4-6 from a family genetics study. The dyslexics had specific deficits in word reading relative to the population mean and verbal IQ, but did not have primary language or motor deficits. Measurements of the posterior temporal lobe, inferior frontal gyrus, cerebellum and whole brain were collected from MRI scans. The dyslexics exhibited significantly smaller right anterior lobes of the cerebellum, pars triangularis bilaterally, and brain volume. Measures of the right cerebellar anterior lobe and the left and right pars triangularis correctly classified 72% of the dyslexic subjects (94% of whom had a rapid automatic naming deficit) and 88% of the controls. The cerebellar anterior lobe and pars triangularis made significant contributions to the classification of subjects after controlling for brain volume. Correlational analyses showed that these neuroanatomical measurements were also significantly correlated with reading, spelling and language measures related to dyslexia. Age was not related to any anatomical variable. Results for the dyslexic children from the family genetics study are discussed with reference to dyslexic adults from a prior study, who were ascertained on the basis of a discrepancy between phonological coding and reading comprehension. The volume of the right anterior lobe of the cerebellum distinguished dyslexic from control participants in both studies. The cerebellum is one of the most consistent locations for structural differences between dyslexic and control participants in imaging studies. This study may be the first to show that anomalies in a cerebellar-frontal circuit are associated with rapid automatic naming and the double-deficit subtype of dyslexia.

Polymorphism of DCDC2 Reveals Differences in Cortical Morphology of Healthy Individuals—A Preliminary Voxel Based Morphometry Study

“…Differences in non-cortical regions included the hippocampus/parahippocampus, amygdala, globus pallidus and putamen. These brain regions correlate with areas identified previously as being involved in reading and/or symbol decoding either structurally or functionally (Kronbichler et al 2007;Brambati et al 2006;Cao et al 2006;Casanova et al 2005;Silani et al 2005;Vinckenbosch et al 2005;Aylward et al 2003;Eckert et al 2003;Ruff et al 2003;Brown et al 2001;Eliez et al 2000;Rumsey et al 1999). …”

“…Compared to structural imaging studies before 2005 (Brambati et al 2004;Eckert et al 2003;Brown et al 2001;Eliez et al 2000), several recent studies, using more optimized and contemporary imaging techniques, have reported mixed patterns of increased and decreased gray matter volumes in dyslexia. More specifically, these studies show increases in GM volume in several cortical areas pertaining to language including: posterior, medial and inferior temporal gyri, precentral and postcentral gyri, superior and medial frontal gyri and precuneus (Kronbichler et al 2007;Silani et al 2005;Vinckenbosch et al 2005).…”

The role of the basal ganglia and cerebellum in language processing

“…They are also consistent with studies that have found abnormal cerebellar morphology or activity in patients with developmental dyslexia and language impairment. Structural MRI studies have shown that the right anterior lobe of the cerebellum is smaller in children with developmental dyslexia and is correlated with reading performance (Eckert et al, 2003). Another structural MRI study reported smaller cerebellar grey matter asymmetry in adults with developmental dyslexia and that smaller asymmetry was correlated with poorer reading performance (Rae et al, 2002).…”

Quantitative temporal lobe differences: Autism distinguished from controls using classification and regression tree analysis

“…Since RD subjects would be expected to have a greater likelihood of temporal lobe anomalies [16,17], the observation that the relationships between temporal lobe structures in RD are more similar to those with autism is not surprising.…”

“…Temporal lobe differences have been reported in subjects with a reading deficit (RD) when compared to typical developing, non-reading impaired controls [16,17]. Furthermore, some have categorized features of the broader phenotype of language impairments in autism as having commonalities with verbal-based learning disabilities [18,19].…”