Dysfunction of the auditory thalamus in developmental dyslexia

Abstract

Developmental dyslexia, a severe and persistent reading and spelling impairment, is characterized by difficulties in processing speech sounds (i.e., phonemes). Here, we test the hypothesis that these phonological difficulties are associated with a dysfunction of the auditory sensory thalamus, the medial geniculate body (MGB). By using functional MRI, we found that, in dyslexic adults, the MGB responded abnormally when the task required attending to phonemes compared with other speech features. No other structure in the auditory pathway showed distinct functional neural patterns between the two tasks for dyslexic and control participants. Furthermore, MGB activity correlated with dyslexia diagnostic scores, indicating that the task modulation of the MGB is critical for performance in dyslexics. These results suggest that deficits in dyslexia are associated with a failure of the neural mechanism that dynamically tunes MGB according to predictions from cortical areas to optimize speech processing. This view on task-related MGB dysfunction in dyslexics has the potential to reconcile influential theories of dyslexia within a predictive coding framework of brain function.functional MRI | speech recognition | auditory processing | magnocellular

Morphometric changes in subcortical structures of the central auditory pathway in mice with bilateral nodular heterotopia

“…Interestingly, a similar pattern of atypical neuronal morphology was also present in the MGN of dyslexics with more small and fewer large neurons [31]. This finding is further supported by recent functional imaging data showing abnormal activity in the region of the MGN in dyslexic individuals during an auditory phoneme discrimination task [34]. Numerous studies also report impaired processing of rapid, but not slow, auditory information in language and reading impaired populations, including SLI and dyslexia, and even at-risk infants [29,[35][36][37][38][39][40][41][42][43].…”

Dysfunction of Rapid Neural Adaptation in Dyslexia

“…Correspondingly, short-term adaptation of auditory and visual cortices to the statistics of noise facilitate perception in animal models (Atiani et al, 2009), and neural adaptation may also support noise exclusion in humans (Parbery-Clark et al, 2011). Third, neural coding deficits in auditory thalamus and brainstem have been found in dyslexia for tasks that use consistent stimulus or noise features (Chandrasekaran et al, 2009; Díaz et al, 2012). Our observation of dysfunction in cortical adaptation suggests these may be systems-level deficits, given corticofugal signaling is responsible for modulating auditory representations in thalamus and brainstem (Chandrasekaran et al, 2014; Suga et al, 2002).…”

Distinguishing cause from effect – many deficits associated with developmental dyslexia may be a consequence of reduced and suboptimal reading experience

“…A number of cross-sectional MRI studies with adults and children have suggested that functional deficits and structural disruptions of the thalamus are a cause of developmental dyslexia (Diaz, Hintz, Kiebel, & von Kriegstein, 2012;Jednoróg et al, 2015;Livingstone, Rosen, Drislane, & Galaburda, 1991;Preston et al, 2010). Skeide et al (2017) recently combined a controlled longitudinal reading intervention with resting-state fMRI in a sample of 30 illiterate Indian adults.…”