Functional neuroanatomical evidence for the double-deficit hypothesis of developmental dyslexia

Abstract

The double-deficit hypothesis of dyslexia posits that both rapid naming and phonological impairments can cause reading difficulties, and that individuals who have both of these deficits show greater reading impairments compared to those with a single deficit. Despite extensive behavioral research, the brain basis of poor reading with a double-deficit has never been investigated. The goal of the study was to evaluate the double-deficit hypothesis using functional MRI. Activation patterns during a printed word rhyme judgment task in 90 children with a wide range of reading abilities showed dissociation between brain regions that were sensitive to phonological awareness (left inferior frontal and inferior parietal regions) and rapid naming (right cerebellar lobule VI). More specifically, the double-deficit group showed less activation in the fronto-parietal reading network compared to children with only a deficit in phonological awareness, who in turn showed less activation than the typically-reading group. On the other hand, the double-deficit group showed less cerebellar activation compared to children with only a rapid naming deficit, who in turn showed less activation than the typically-reading children. Functional connectivity analyses revealed that bilateral prefrontal regions were key for linking brain regions associated with phonological awareness and rapid naming, with the double-deficit group being the most aberrant in their connectivity. Our study provides the first functional neuroanatomical evidence for the double-deficit hypothesis of developmental dyslexia.

An examination of the rapid automatized naming–reading relationship using functional magnetic resonance imaging

“…have used neuroimaging techniques to study the neural activation during RAN (e.g., Breznitz, 2005;Christodoulou, 2010;Gonzalez-Garriod, Gomez-Velazquez, Zarabozo, Ruiz-Villeda, & de la Serna Tuya, 2011;Misra, Katzir, Wolf, & Poldrack, 2004;Wiig et al, 2002) and the neural relationship between RAN and reading (e.g., He et al, 2013;Norton et al, 2014;Turkeltaub, Gareau, Flowers, Zeffiro, & Eden, 2003). To our knowledge, only one study has investigated the neural circuitry of RAN using fMRI (Misra et al, 2004).…”

“…First, RAN appears to activate a general language network that includes occipital, temporal, parietal, and frontal regions (Misra et al, 2004). Second, behavioural RAN performance is associated with reading-related neural activity and grey matter volume within the language network (Christodoulou, 2010;He et al, 2013;Norton et al, 2014;Turkeltaub et al, 2003). Third, the cerebellum is consistently reported as a structure in which the RAN-reading relationship is found (Eckert et al, 2003;He et al, 2013;Norton et al, 2014;Turkeltaub et al, 2003).…”

“…We used previous literature to guide our selection of left lateralized regions known to be involved in basic reading processes (Indefrey & Levelt, 2004;Price 2012), speech production (Guenther et al, 2006), and RAN (He et al, 2013;Norton et al, 2014;Turkeltaub et al, 2003). We then verified that there was activity in each literature driven region of interest for two or more of the task specific mean activation maps.…”

How many tests do you need to diagnose Learning Disabilities?

“…Reading, writing and doing mathematic are complex and slowly learned skills requiring the integration of multiple visual, linguistic, cognitive and attentional processes (Norton et al, 2014).…”

Coherence: The Measurement and Application of Brain Connectivity

“…However, after participating in different reading interventions, a difference in frontal connectivity no longer existed. Futhermore, recent literature suggests children with double-deficits (phonological and rapid naming deficits) have more atypical brain connectivity than children with only a single deficit (Norton et al, 2014), which demonstrates an additive relationship between atypical connectivity and learning problems. These findings indicate treatment outcomes of children with dyslexia, in comparison to a control group, are dependent on the normalization of brain connectivity in specific regions of the brain (Richards & Berninger, 2008)-a concept that has major implications for directing future neurological interventions, such as coherence-based neurofeedback.…”