Right hemisphere participation in aphasia recovery : a qualification of incongruous findings in the literature

Neuroplasticity research yields mixed results for the differential contribution of perilesional and contralesional brain areas to language recovery in aphasia. This paper will outline variables that mediate the presence and degree of right hemisphere activity and may account for some of the inconsistent research findings. Factors include the site and size of left hemisphere lesions, the phase of recovery, and the language task type and complexity. The performance accuracy of tasks also will be explored to further qualify the nature of homologous activity. Results found right hemisphere activation to be modulated by the damage and preservation of specific brain areas as well as by the presence of large left hemisphere lesions. Right hemisphere activity also was more consistently evident in the acute phase of recovery and returned to the left hemisphere in the chronic stage. Additionally, homologous areas tended to be more active during comprehension-based language tasks and during tasks of greater difficulty. In qualifying the nature of contralesional mechanisms, the activity appears to be more linguistic-oriented in less-recovered individuals with aphasia and more related to cognitive effort in well-recovered individuals. The nature of homologous activation depends on the brain’s ability to reactivate left hemisphere language networks.