Investigation of magno- and parvo-cellular pathways in developmental dyslexia

Investigation of magno- and parvo-cellular pathways in developmental dyslexia

First Author: Chiara Andreola -- Child Psychopathology Unit, Scientific Institute, IRCCS Eugenio Medea
Additional authors/chairs: 
Sara Mascheretti; Denis Peruzzo; Vittoria Trezzi; Andrea Nordio; Cecilia Marino; Filippo Arrigoni
Abstract / Summary: 

Purpose: According to the visual magnocellular (M) deficit theory of developmental dyslexia (DD), the M stream may represent a correlate of reading acquisition, reading failure and (dis)ability. This study assesses with fMRI the modifications occurring in the M and parvocellular (P) pathways in a cohort of Italian children affected by DD.
Method: Fourty-six children participated in this study: 23 subjects with DD (age:14.2±1.5; f/m:6/17) and 23 typical readers (TR) (age:12.8±1.6; f/m:8/15). Each subject underwent a 3T fMRI with visual stimulation in a block-design. Both M and P stimuli were full-field sinusoidal gratings with sinusoidal counterphase flicker. The M stimulus was a 100% luminance contrast, black-white grating with a spatial frequency of 0.5cpd and a flicker frequency of 15Hz. The P stimulus was a low luminance-contrast, high color-contrast red-green grating with a spatial frequency of 2cpd and a flicker frequency of 5Hz.
One-tailed t-test analysis were performed with age, socio-economic status and ADHD scores as covariates.
Results: When comparing activations during the M and P stimuli, subjects with DD showed significant (p<0.05 FDR-corrected; cluster size >15 voxels) reduced activations in bilateral parietal dorsal stream, in left superior frontal gyrus, caudate nucleus and insula, and in right angular and middle temporal gyri, during the M stimulus.
Conclusions: As expected, subjects with DD showed reduced activations in areas involved in visual processing, attention, language and accessing word meaning while reading, under the M condition. These results indicate the M stream as a correlate of reading.