Therapy-induced neuroplasticity in chronic aphasia

Research on the neural substrate of aphasia recovery has consistently increased since the advent of functional neuroimaging. The evidence from therapy-induced aphasia recovery studies shows that better recovery results from the reactivation of left hemisphere function; still, the specific left hemisphere key areas that sign successful outcome with a specific therapy approach remain to be identified. Nine participants suffering from aphasia received brief and intensive therapy with Semantic Feature Analysis (SFA). Behavioural and neuroimaging data during overt picture naming were obtained prior to and after therapy. This paper reports on a group of participants having benefited from SFA, and two distinct patterns of improvement. Correlational analysis showed that differences in outcome were not related to lesion size, but were negatively correlated with damage to Broca's area (BA45). Moreover, a group analysis showed that therapy-induced recovery following SFA was characterized by (a) a significant correlation between improvement and activation in the left precentral gyrus (BA4/6) before therapy, and (b) the recruitment of the left inferior parietal lobule, an area known for its role in semantic integration, following therapy with SFA. Individual fMRI analyses showed that although adaptive brain plasticity appeared to operate differently in each patient, best responders to SFA therapy recruited less areas after training compared to participants having shown less recovery who showed a larger number of activated areas sustaining recovery. The results of the present study suggest that a significant activation of BA4/6 could indicate the use of SFA to achieve successful outcome. Also our results suggest that greater SFA improvement in chronic aphasia is associated with recruitment of areas in the left hemisphere.