Functional plasticity in Alzheimer's disease: effect of cognitive training on language-related ERP components.

Starting from the observation of a reduced gray matter in the inferior temporal regions of Alzheimer's disease (AD) patients, the present study hypothesized an altered language-related functional activity in left occipito-temporal areas in AD, and the possibility of a plastic change of these regions induced by an intensive cognitive training. To this aim, eleven mild/moderate AD underwent to a 5-week cognitive training (40 h). Before and after the training, evoked potentials were recorded from 26 scalp electrodes during a lexical decision task which required word/no-word discrimination. Stimuli included high- and low-frequency words and non-words, and the recognition potential (RP) together with the N400 have been analyzed and compared with those collected from a matched healthy control group. Results comparing controls and patients before training showed a normal RP in AD patients with a clear peak over left occipito-temporal sites. In addition, controls exhibited a left anterior lateralization of N400 component to words and an inverted pattern for non-words, whereas an altered N400 with bilateral distribution at both word and non-word conditions was found in AD patients. After the cognitive training, AD patients did not show changes in the N400, but revealed a significant enhanced amplitude of RP to high-frequency words. Behavioral responses to the lexical decision task and scores from neuropsychological tests did not evidence improvements nor worsening after training. These data point to an intact functionality of left posterior linguistic networks in mild/moderate AD, and the possibility to increase plastically their activity after a cognitive training.