Word and number reading in the brain: evidence from a voxel-based lesion-symptom Mapping study

The high incidence of number transcoding deficits in aphasic subjects suggests there is a strong similarity between language and number domains. However, recent single case studies of subjects who showed a dissociation between word and number word transcoding led us to hypothesize that the two types of stimuli are represented independently in the cognitive system. Moreover, it is still unclear whether word and number word reading rely on different brain areas. The present study was designed to investigate this issue in a group of 20 left hemispheric stroke patients who were all tested on Arabic number, number word and word reading (all stimuli were matched for frequency and length). To identify which brain lesions affected performance on the three tasks, we analyzed patients' lesions and behavioural performances using Voxel-based Lesion-symptom Mapping. With this technique, several t-tests can be performed at each voxel to compare behavioural performances of patients with and without a lesion affecting that voxel. Results showed that Arabic number and number word reading involve the same damaged structures, primarily located in the temporo-parietal regions, whereas word reading relies on a frontal network that includes the superior part of Broca's area and the premotor cortex. These data complement the existing neuropsychological literature by suggesting that the already reported dissociations between word and number word reading are supported by distinct cortical networks.