Electromagnetic brain activity in higher frequency bands during automatic word processing indicates recovery of function in aphasia

Abstract

AIM: Little is known about how treatment affects the neural substrate of language function in stroke sufferers. In the present study authors investigated neuronal correlates of treatment induced recovery of language functions in patients with chronic aphasia. METHODS: In 10 chronic aphasia patients and 10 age- and gender-matched control participants, evoked high-frequency activity (HFA, >20 Hz) was determined from the magnetoencephalogram in an automatic word recognition task, in which content, function, and pseudowords were visually presented at fast rate (350-ms). Recording was repeated after 2 weeks, in aphasics after intensive language training to evaluate training effects, in controls to establish HFA stability. RESULTS: In the first recording, bilateral HFA distribution in controls contrasted right-hemispheric predominance in the patients. After training, this right>left asymmetry in aphasics was reduced to a bilateral pattern similar to controls. While word class did not substantially affect HFA patterns in the two groups, enhanced right-hemispheric HFA in the patients varied with better language function (test performance) prior to training, while after training, left-temporal function- and pseudoword evoked HFA varied with performance in tests of written language. CONCLUSIONS: Results suggest that HFA might serve as a measure in the evaluation of rehabilitation efforts in chronic aphasia: enhanced right-hemispheric HFA might indicate compensatory activation of contralateral language areas, which tends towards patterns comparable to normal subjects after effective language training.