Brain activity in visual cortex correlates with Chinese reading performance

Abstract

Becoming literate is one of the most important achievements in childhood. Considerable evidence has suggested that phonological processing skills play a crucial role in beginning reading (Ehri, 1998). The role of visual processing skills, however, remains inconclusive. Psychophysical and neurophysiological studies have demonstrated that dyslexic children and adults were impaired in tasks that involved temporal processing and motion sensitivity, such as contrast sensitivity, velocity discrimination, spatio-temporal integration, and motion direction discrimination (Demb et al., 1998; Eden et al., 1996; Lovegrove et al., 1980). These findings implicate that impairments in visual processing of dyslexic individuals are due to dysfunctions in area V5/MT, a region in the dorsal visual pathway in the brain, which is dominated by input from magnocellular (M) cells in illumination and motion detection (Desimone & Ungerleider, 1986; Newsome et al., 1989). The Magnocellular theory postulates that disruption in the M pathway leads to deficiencies in visual processing and to abnormal binocular control and visuospatial attention (Stein, 2001). However, this theory has been challenged by recent neurobiological and psychophysical findings. Some researchers concluded that only a minority of dyslexics seems to have a magnocellular dysfunction and that visual and motor factors are not associated with reading development (Ramus et al., 2004). In this study, we used functional magnetic resonance imaging (fMRI) to investigate whether brain activity during visual motion processing is associated with the ability to read in Chinese. We scanned 26 normal Chinese beginning readers (age: 7) when they performed a visual motion discrimination task. Brain activation from children (n = 13) whose reading performance was above average was significantly stronger in MT compared to brain activation from children (n = 13) whose reading was below average. This finding from normal readers provides compelling evidence for the M pathway theory of reading development and dyslexia.