Functional imaging studies of treatment-induced recovery in chronic aphasia

Background: The reacquisition of language after stroke may profit from intense training with several hours of language exercises provided on each training day, especially in the chronic stage. Despite the general effectiveness of this, few studies to date have examined which brain regions mediate successful language recovery as a result of intense training. This knowledge is particularly important because the necessity of several hours of language exercises each day draws a considerable amount of (a) attentional and cognitive resources from the patients and (b) financial and personnel resources from the health system. Aims: Not all aphasia patients may be equally suited for intense training approaches. Functional imaging studies of treatment-induced recovery in chronic aphasia may provide answers to this question and may allow the target-oriented allocation of aphasia patients to (intense) training in the future. In the following sections we will provide a comprehensive review of functional imaging studies that employed intervention paradigms to explore the reacquisition of language functions in chronic aphasia. Main Contribution: A total of 13 studies have been published so far, including a total of 57 chronic aphasia patients. Most of these studies comprised case reports (N=1-3 patients), which preclude generalisation of the results. To date, only three group studies (N=10/11/16) have been accomplished. The majority of studies reported treatment-induced changes of activity in both hemispheres, indicating that both perilesional as well as right (frontal) brain regions mediate intense training success. As 10 of the studies reviewed were concerned with the remediation of word-retrieval difficulties, little is known of how treatment impacts on other aspects of impaired language functions like reading, comprehension, or syntactic processing. Furthermore, only immediate training effects were examined, and brain regions related to the long-term retention of treatment effects may be different. Conclusions: More methodologically sound group studies are required to determine the neural correlates of treatment-induced recovery in the chronic stage of aphasia. Supplemented by other imaging techniques, this knowledge may eventually contribute to the target-oriented allocation of treatment resources in aphasia patients and may increase treatment efficiency.