Reading disorders and weak Verbal IQ following left hemisphere stroke in children: no evidence of compensation

Children who suffer a left-hemisphere (LH) stroke do not appear to experience the verbal deficits that are apparent in adults with similar lesions. To explain these findings it has been suggested that the plasticity of the developing brain enables homologous areas in the right hemisphere (RH) to compensate for LH weakness. In this paper we find evidence against this theory from investigations into the effect of LH and RH lesions on intelligence and literacy skills in a group of children with unilateral postnatal stroke. At group level, there was no significant effect of LH stroke on Verbal IQ (VIQ) or upon reading ability, when compared with RH stroke. But at the individual level, the majority of children with LH stroke achieved standard scores below average, with some below -2 SD. The standard scores of children with RH lesions were normally distributed, showing no detrimental effect that would indicate compensation. Large discrepancies between VIQ and Performance IQ (PIQ), in both directions, were also a characteristic of the LH group. Using normative data that we collected on the reading of irregular and regular words and nonwords, we identified patterns of phonological and surface dyslexia in both lesioned groups. We argue that LH stroke reduces the efficiency of verbally-related skills, but that the processes available to children with postnatal lesions are those available to normally developing children, and that these can entail processes in either hemisphere.