What bilateral damage of the superior parietal lobes tells us about visual attention disorders in developmental dyslexia

Neuroimaging studies have identified the superior parietal lobules bilaterally as the neural substrates of reduced visual attention (VA) span in developmental dyslexia. It remains however unclear whether the VA span deficit and the deficits in temporal and spatial attention shifting also reported in dyslexic children reflect a unitary spatio-temporal deficit of attention - probably linked to general posterior parietal dysfunction- or the dysfunction of distinct attentional systems that relate to different neural substrates. We explored this issue by testing an adult patient, IG, with a specific damage of the bilateral superior parietal lobules after stroke, on tasks assessing the VA span as well as temporal and spatial attention shifting. IG demonstrated a very severe VA span deficit, but preserved temporal attention shifting. Exogenous spatial orientation shifting was spared but her performance was impaired in endogenous attention. The overall findings show that distinct sub-systems of visual attention can be dissociated within the parietal lobe, suggesting that different attentional systems associated with specific neural networks can be selectively impaired in developmental dyslexia.