Event-related potentials indicate bi-hemispherical changes in speech sound processing during aphasia rehabilitation.

OBJECTIVE To investigate changes in brain activation related to tone and speech sound processing during aphasia rehabilitation. DESIGN Longitudinal study investigating patients with stroke, subarachnoid hemorrhage and traumatic brain injury 3 and 7 months post-injury. SUBJECTS Eight patients with aphasia, reflecting a wide range of auditory comprehension impairment. METHODS Token test and Norwegian Basic Aphasia Assessment were used to measure auditory comprehension function. Brain event-related potentials were recorded in passive paradigms with harmonically rich tones and syllables in order to obtain the mismatch negativity component that reflects automatic stimulus discrimination. In an active syllable discrimination paradigm, stimulus feature integration (N1), attended stimulus discrimination and classification (N2), and target detection (P3) were studied. RESULTS Auditory comprehension scores improved approximately 10% during the observation period. Ipsilesional frontal P3- and N2-amplitude increased significantly. A significant shift in topographical distribution from the contralesional to the ipsilesional hemisphere was observed for the N2 component. The study of individual waveforms indicates inter-individual differences in reorganization after brain injury. CONCLUSION Hemispherical distribution of brain activation correlating with speech sound processing in aphasia can change during the first months after brain injury. Event-related potentials are a potentially useful method for detecting individual activation patterns relevant to recovery in aphasia rehabilitation.